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Biomechanics of stair walking and jumping a
David J. Loy & Arkady S. Voloshin
a b
a
Department of Mechanical Engineering and Mechanics and Institute for Biomedical Engineering and Mathematical Biology , Lehigh University , Bethlehem, PA, 18015, USA b
Department of Mechanical Engineering and Mechanics , Lehigh University , 354 Packard Lab No. 19, Bethlehem, PA, 18015, USA Published online: 14 Nov 2007.
To cite this article: David J. Loy & Arkady S. Voloshin (1991) Biomechanics of stair walking and jumping, Journal of Sports Sciences, 9:2, 137-149, DOI: 10.1080/02640419108729875 To link to this article: http://dx.doi.org/10.1080/02640419108729875
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Journal of Sports Sciences, 1991, 9, 137-149
Biomechanics of stair walking and jumping DAVID J. LOY and ARKADY S. VOLOSHIN* Department of Mechanical Engineering and Mechanics and Institute for Biomedical Engineering and Mathematical Biology, Lehigh University, Bethlehem, PA 18015, USA
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Accepted 12 December 1989
Abstract
Physical activities such as stair walking and jumping result in increased dynamic loading on the human musculoskeletal system. Use of light weight, externally attached accelerometers allows for in-vivo monitoring of the shock waves invading the human musculoskeletal system during those activities. Shock waves were measured in four subjects performing stair walking up and down, jumping in place and jumping off a fixed elevation. The results obtained show that walking down a staircase induced shock waves with amplitude of 130% of that observed in walking up stairs and 250% of the shock waves experienced in level gait. The jumping test revealed levels of the shock waves nearly eight times higher than that in level walking. It was also shown that the shock waves invading the human musculoskeletal system may be generated not only by the heel strike, but also by the metatarsal strike. To moderate the risk of degenerative joint disorders four types of viscoelastic insoles were utilized to reduce the impact generated shock waves. The insoles investigated were able to reduce the amplitude of the shock wave by between 9% and 41% depending on the insole type and particular physical activity. The insoles were more effective in the reduction of the heel strike impacts than in the reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping trials than in the stair walking studies. The insoles were ranked in three groups on the basis of their shock absorbing capacity. Keywords: Shock absorption, jumping, stair climbing, viscoelastic insoles, dynamic loading, accelerometry.
Introduction
The human's environment is constantly changing from that of the natural grounds of the countryside to that of the concrete and asphalt reality of the modern industrial city. Another change encountered by the human in modern life styles is climbing up and down staircases, especially in office buildings. These alterations of the surroundings and fitness habits have resulted in much higher physical loads on the human musculoskeletal system even during normal everyday activities (Simon et al., 1972; Wosk and Voloshin, 1981). A recent comparative study showed that running on an asphalt surface generated shock *Send all correspondence to: Professor Arkady Voloshin, 354 Packard Lab No. 19, Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015, USA. 0264-0414/91 $03.00 + .12 © 1991 E. & F.N. Spon Ltd.
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waves with 40% higher amplitude than running on a grass surface (Loy, 1987). Several authors (Miller and Power, 1981; Steben and Steben, 1981) recommend drop jumping as an effective exercise for athletes who prepare themselves for explosive activities, such as sprinting and jumping. The impulsive loads to which the foot is subjected during any of those activities may be considerably higher than the individual's body weight, depending on gait velocity, degree of jumping and viscoelastic properties of the foot (Stanish, 1977). Because of these higher dynamic forces, the natural shock absorbers of the human musculoskeletal system may become insufficient. The impulsive energy which invades the body during each heel strike can no longer be sufficiently attenuated, modified and dissipated by the body's shock absorbers. This tends to an overloading of the natural shock absorbers of the human musculoskeletal system (Light et ah, 1980; Simon et ai, 1981; Voloshin and Wosk, 1982). The natural shock-absorbing structures in the musculoskeletal system are characterized by a viscoelastic time-dependent mechanical behaviour, which may become ineffective in withstanding sudden impulsive loads (Folman et ah, 1986; Radin et al., 1972). Degenerative joint diseases may thus be seen as a late clinical result of fatigue failure of the natural shock absorbers, submitted to the intermittent impacts over a period of time (Radin et al, 1972). Walking, running, and jumping are the common daily activities which introduce impacts of this nature into the locomotor system. Previous research has clearly shown a correlation between the cyclic impact loading on the absorbing joints and the degenerative process in their tissues (Dekel and Weissman, 1978; Radin et al., 1978). Even under normal physiological conditions, the intermittent and continuously repetitive onslaught of shock waves invading the locomotor system during gait tends to cause a slowly progressive weakening of the natural shock absorbers and may lead to headaches, lower back pain, degenerative joint disorders, and even osteoarthritis (Folman et al, 1986; Freeman, 1975; Voloshin and Wosk, 1982). Obviously, the higher impulsive cyclic loads generated during jumping and stair climbing will contribute to the progression of this degenerative process. Other related injuries stemming from sports utilizing jumping motions tend to occur in the hip and pelvic regions of the human musculoskeletal system (Clancy, 1980). These injuries were focused upon by a previous study which was retrospectively assessed at a general sports medicine clinic over a 2-year period (Lloyd-Smith et al., 1985). The three most common bone injuries were sacroiliitis, pelvic and femoral neck stress fractures, and osteitis pubis. The three most common soft-tissue injuries were gluteus médius strain/tendinitis, trochanteric bursitis and hamstring strain (Clancy, 1980; James et al., 1978; Lloyd-Smith et ah, 1985). Overuse accounted for 82.4% of the injuries recorded which were most commonly a result of the higher than normal impulsive loads experienced from running, fitness classes and racquet sports. The treatment of these individuals generally consisted of modified activity, local muscle rehabilitation, heel lifts and/or viscoelastic insoles, change of footwear, and a gradual reintroduction of the specific physical activity. Obviously, the significant reduction or even elimination of the injurious effects of the shock waves are contingent upon the development of accurate methods to quantify these waves and the effect of various shock absorbing insoles on the human body. The results from previous studies showed that the use. of viscoelastic insoles during normal walking can decrease the amplitude of the shock wave propagating through the body and, therefore protect the joints from overloading their capacity to sustain intermittent loading (Light et ah, 1980; Voloshin and Wosk, 1981). The main aim of this study was to use a non-invasive methodology in vivo to evaluate the impulsive loads experienced by the human musculoskeletal system during normal jumping and stair climbing. An evaluation of the
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shock absorbing capacity of different insoles during those physical activities was also performed.
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Methodology This investigation utilized a novel approach, by which a small low-mass PCB piezoelectric accelerometer was placed on the skin surface of the tibial tuberosity (Voloshin et al, 1981). The accelerometer was externally fixed to the human subject with adhesive tape and a tightly wrapped elastic bandage in order to provide measurements as close as possible to an actual bone acceleration during stair walking and jumping. Such attachment of the accelerometer caused the natural frequency of the recording instrumentational set-up to exceed that observed in stair walking and jumping, thus avoiding error due to resonance (Ziegert and Lewis, 1979; Loy, 1987). Comparison of the acceleration amplitude measured by a skinmounted accelerometer to the one rigidly attached to the bone by screws showed differences below 5%. Those experiments were performed in vitro on a fresh cadaver's leg subjected to a simulated loading representing heel strike (Voloshin and Simkin, 1989). The signal was acquired by a TEAC MR-30 multi-channel analogue data cassette recorder and play back unit, with a frequency bandwidth of DC to 1250 Hz. The input was simultaneously monitored with a digital oscilloscope (BK Precision Model 2520, Dynascan Corp.). The signal from the accelerometer was low-pass filtered with the cut-off frequency of 120 Hz. These tapes were then digitized using a personal computer (Zenith 158) modified into a high-speed multi-channel data acquisition and storage system. A Metrabyte Dash-16 (12 bit resolution) A-D converter was utilized to quantify the analogue data prior to recording into data files. The sampling rate was 1000 Hz, ensuring an accurate representation of the filtered signal. Four males in their early 20s (range 20 to 22 years) served as test subjects for both parts of this study. After recording the subject information, each individual was allowed 20 to 40 min to get used to walking naturally up and down the test staircase while connected to the recording instrumentation. At this time, the cable connections, accelerometer placements, and their responses were checked. Each subject then walked four trials up the staircase, all subjects using the same pair of hard heel test shoes (without insole). Most trials usually generated between eight and nine steps of recorded data. This was then followed by four trials of walking up the staircase for each particular pair of viscoelastic insoles to be tested. Afterwards, the same procedure was then repeated for the trials which entailed walking down the staircase. In the next part of the study the impact acceleration data from the tibial tuberosity was acquired using the same subjects and instrumentation during jumping. Each subject jumped up and down in place to generate 30 to 40 sets of data while using the same pair of test sneaker (no-brand name tennis shoe) without insole. This was followed by 30 to 40 trials of jumping in place for each of the same set of viscoelastic insoles tested during the stair walking portion of this study. The subjects were trained to jump repetitively and consistently to the same height above the ground each time (approximately 0.3 m). It was also very important to have the subjects jump and land with as similar a motion as possible. Moreover, any trial that was subjectively determined to be inconsistent with the general trend was discarded and repeated. After the study of jumping in place was completed, the impact of landing was investigated further by having each subject jump naturally from a standing position off a chair platform
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approximately 0.4 m above the ground. The shock absorbing capacity of the same set of viscoelastic insoles was also tested and evaluated for jumping down. Four types of viscoelastic insoles were utilized in this study to reduce the impact shocks generated during stair walking and jumping tests. The insoles A and B were thick composite type insoles contoured to the bottom of the foot and contained portions of viscoelastic material embedded into the urethane foam construction. The type A insole had the viscoelastic material both under the heel (8 mm thick) and metatarsal area (4.5 mm thick) of the insole, while the type B insole had the viscoelastic material under the heel only (6.5 mm thick). The insoles type C and D were of a less complex design. The type C insole was of a plane, thin design, except for the heel (6 mm thick). The insole was constructed entirely of viscoelastic material. The type D design was similar to that of the type A composite insole, with viscoelastic material located under the heel (6.5 mm thick) and metatarsal regions (3.5 mm thick). However, the grooved indentations in these viscoelastic portions of the insole were relatively small. The footwear and insoles were consistently fitted prior to data collection. All subjects used the same footwear and the same set of insoles. The order of the viscoelastic insoles being tested was randomly changed for each subject. The jumping portion of this study took place in a corridor with the floor consisting of poured concrete covered with floor tiles. In the stair walking case, the walking length of each trial was a climb of nine stair steps resulting in a total elevational rise of 1.7 m. The subjects' average gait velocities during these tests were adjusted to approximately 0.91 step s" 1 going up stairs and 1.1 step s" 1 heading down stairs.
Results and Discussion Stair walking The acceleration data recorded while stair walking showed differences in the gait pattern motions between those experienced while walking up or down a staircase and that of walking on level ground. A typical accelerogram recorded from the tibial tuberosity of a subject walking on level ground wearing hard heel test shoes (without insoles) is presented in Fig. 1. The subject's walking style was similar to the patterns observed in the previous level ground gait studies (Loy, 1987; Voloshin, 1988). The usual sequence of events observed in a level gait pattern proceeds with the large steep heel strike (approximately 3.0 g in this case) followed closely by a small positive double peak bulge (usually 0.1 s after heel strike) containing the insignificant metatarsal strike and push-off. Another feature observed in this type of gait pattern, is that of the acceleration resulting from the toe-off of the leg. This event occurs at about half the time between successive heel strikes (approximately 0.5 s after heel strike). In contrast, the gait pattern recorded for walking up a staircase does not have heel strike present as is the case with level ground gait. The heel of the foot never makes contact with the stair when going up the staircase. The biomechanics of the gait motion while walking up stairs is different because only the metatarsal part of the foot makes contact with the ground (stair) during each step. In addition, there is usually little space on the step to place a whole foot. Those metatarsal strikes, as seen at 0.25 and 1.25 s in Fig. 2a, are of higher magnitude (approximately 5.9 g) and less slope than that of the heel strike experienced during normal gait on level ground. The impulsive loads experienced in climbing stairs at roughly the same gait velocity were over 180% of that observed for level gait. It is interesting that there was no
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LEFT TIBIA RESPONSE DURING GAIT »/o INSOLE
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3.00..
-2.00..
-3.001
Fig. 1. Accelerogram of a level gait observed at the subject's left tibial tuberosity. reaction from the opposing leg's impact seen in the accelerogram for walking up stairs. This seems puzzling since the strike magnitudes are so much greater than that experienced on level ground. Even though it may take more studies to determine the reasoning for this occurrence, the unorthodox leaning positioning experienced by the human body during stair climbing and the bend at the knee joint are strongly suspected as the cause. The gait pattern observed for walking down stairs (Fig. 2b) does show a similar opposing heel strike reaction phenomenon as previously observed in the level gait pattern. Even so, the biomechanics of walking down stairs is significantly different from that observed for normal gait on level ground or climbing up stairs. The metatarsal of the foot makes the first contact with the stair during walking down stairs as was the case in walking up a staircase. However, the metatarsal strike does not usually generate the same impulsive magnitudes seen during gait going up stairs. Even though the metatarsals touch the stair first, the body is not brought to a complete stop on that step until the heel strike impact occurs. This can be clearly seen in the accelerogram for walking down a staircase (Fig. 2b). The heel strikes of approximately 7.8 g occur at 0.25 s and 1.15 s and are preceded by a couple of small positive peaks (around 1.0 g) resulting from the action generated by the metatarsal contact during this portion of the support phase. Moreover, the impact strike magnitudes generated during walking down a staircase were nearly 130% greater than that observed in walking up stairs and 250% greater than that experienced in normal level gait (Loy, 1987), as shown in Fig. 3. This indicates that the physical action of walking down stairs results in higher dynamic loads on the human musculoskeletal system than that of walking up stairs and even more so than walking on level ground. To moderate the increased dynamic load on the human musculoskeletal system, four different types of viscoelastic insoles were utilized to reduce the impact shocks generated during stair walking. The acceleration amplitudes measured at the tibial tuberosity (Table 1) indicated overall reduction of the dynamic loading on the human musculoskeletal system while using in-shoe viscoelastic insoles. In the most extreme case, the type A insole was nearly
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7.5 _
WALKING UP A STAIRCASE t/t INSOLE
Time (S ) WALKING DOWN A STAIRCASE n/o INSOLE
1.5
Ti me CS; 1 -5.9 1 Fig. 2. Acceleration pattern recorded at the left tibial tuberosity of a subject walking (a) up and (b) down a staircase.
three times more shock-absorbing than the type C insole for either type of stair walking. The designed moulded grooves present in the viscoelastic portions allowed the viscoelastic material to flow more freely when worn in the constrictions of the shoe, thus giving the insole better damping properties (Table 1). The percent attenuation values shown in Table 1 reflect the average value for the four subjects tested. The percent attenuations were calculated from the mean metatarsal strike values for the up stairs trial and from the mean heel strike values for the down stairs trial. The 'without insole' values were used as the basis in both cases. Even though the insoles tested in this study significantly reduced the impact shocks in both stair gait types, it is quite clear that the insoles were more shock absorbing in walking down stairs
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Acceleration (g)
8 -
m
6
H
S
walking up
walking down
4
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2
level gait
Fig. 3. Acceleration values in level walking and stair climbing.
Table 1. Attenuational shock capacity of viscoelastic insoles in stair walking Insole type w/o A B C D
Insole type w/o A B C D
Walking up a staircase Metatarsal strike (mean + s.D.) in g iinits
Number of trials
Subject no. 1
Subject no. 2
34 34 34 34 34
5.45 + 0.42 3.98 ±0.38 4.24 + 0.39 4.94 + 0.43 4.36+0.41
6.49 ±0.71 4.66 + 0.56 4.91 ±0.47 5.75 ±0.60 4.98 + 0.54
Number of trials 34 34 34 34 34
Percent Subject no. 3 Subject no. 4 attenuation 6.13 + 0.63 4.42 + 0.56 4.75 + 0.46 5.53+0.62 4.83 + 0.53
5.16±0.49 N.A. 3.86+0.43 27.06 ±1.36 4.12±0.37 22.30+1.71 4.71 ±0.51 9.86+1.22 4.15±0.48 21.01 ±1.66
Walking down a staircase Heel strike (mean + s.D.) in g units Subject no. 1 Subject no. 2 7.83 ±0.67 4.60 ±0.42 5.43 ±0.49 6.65±0.51 5.76 ±0.53
8.70 ±0.93 4.85 ±0.54 5.80+1.20 7.14 ±1.48 6.22 ±0.94
Percent Subject no. 3 Subject no. 4 attenuation 6.58+0.73 3.73+0.91 4.48 + 0.57 5.51+0.67 4.89 + 0.38
7.00 ±0.94 4.33 ±0.68 5.04±0.69 5.65 ±0.99 4.96±0.53
N.A. 41.73 ±2.72 30.96 ±2.28 17.14+1.85 27.44 ±1.65
than in walking up stairs. This was not that surprising since the insole designs were mainly focused upon the reduction of the well known heel strike rather than that of the newly recognized metatarsal strike. Also, these modifications of the impact shocks can be clearly seen by comparing the recorded stair gait accelerograms of both the 'with insole' (Figs 4a and 4b) and 'without insole' cases (Figs 2a and 2b). Jumping The next phase of this work dealt with the biomechanical aspects of jumping. The same set of viscoelastic insoles as utilized in the stair walking was tested in both types of jumping.
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7.5 ,.
-2. S l 10. 0 _
WALKING UP A STAIRCASE
Time CS 1 WALKING DOWN A STAIRCASE
Time (S ) -5.0 1 Fig. 4. Acceleration signal recorded at the left tibial tuberosity of a subject walking (a) up and (b) down a staircase using type A insoles. The accelerograms of signals recorded from the tibial tuberosity of the subject while jumping in place wearing test sneakers with and without viscoelastic insoles are shown in Figs 5b and 5a respectively. The jumping patterns are essentially the same except for the significant reduction in impulsive strike magnitudes by an insole. There are two sets of impulsive strikes observed in the accelerograms for jumping in place. The first set of these impulsive strikes was associated with the landing phase. It can be seen clearly as the leading sets of uneven double spikes (first peak - 20.0 g, second peak - 15.5 g) occurring at 0.25 and 0.85 s (Fig. 5a). The second set of impulsive strikes, located at 0.35 and 1.0 s (Fig. 5a), was associated with the push-off motions for the next successive jump.
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Biomechanics of stair walking and jumping 25
-° T
TIBIA RESPONSE TO JUMPING IN PLACE
(a)
15.0 .
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5.0
-5.0 ..
Time IS I -15.0
2S
1
-° T
TIBIA RESPONSE TO JUMPING IN PLACE
(b)
15.0 ..
5.0 ..
a a a
—»
1.5
-5.0 ..
Time IS ! -IS.O 1 Fig. 5. Acceleration pattern recorded on the tibial tuberosity of a subject jumping in place (a) without insoles and (b) with insoles.
The landing phase observed in the accelerograms for jumping in place usually contained two peaks. The first peak was the metatarsal strike followed closely (approximately 50 ms) by the heel strike. This is the reverse order of strikes observed in level walking patterns. The impact magnitudes of these peaks vary according to the way an individual lands on his feet. One who lands mostly on the metatarsal and less on the heel of the foot would have a higher first peak followed by a significantly smaller second peak. Alternatively, one who lands lightly on the metatarsal and more on the heel of the foot would have a smaller first peak followed by a higher second peak. Thus, depending on the individual landing pattern, there is a countless combination of double strike values possible for jumping in place.
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While the landing phase of jumping in place had two distinct peaks, the landing in the jumping down usually only had one major peak which was clearly associated with the heel strike. This can be seen in the accelerograms recorded for jumping down (Figs 6a and 6b). An interesting observation seen for both the stair walking and jumping studies was that an individual tended to land more with the metatarsal of the foot when needing a propelling forward push-off for the next successive step or jump (as with jumping in place and walking up stairs), and more with the heel of the foot when coming to a more complete stop on the
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25.0 „
TIBIA RESPONSE TO JUMPING DOWN
(a)
_
15.0 .
o> c o
—
5.0
.,
1.5
-5.0 .. o
-15.0 ..
Time (S )
-25.0 1 25.0 ,.
TIBIA RESPONSE TO JUMPING DOWN
(b)
_
15.0 ..
c a
—
5.0
1.0
S -5.0
-15.0 ..
1.5
Time IS 1
-25.0 1
Fig. 6. Acceleration pattern recorded on the tibial tuberosity of a subject jumping down (a) without insole and (b) with insole.
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ground or steps (as with jumping down and walking down stairs). The strike magnitudes of either type of jumping are five to ten times greater than those experienced during level gait. Thus, the individuals who avidly participate in sport activities which contain significant amounts of jumping (i.e. basketball, aerobics and so on) may expose their musculoskeletal system to accelerated risk of degenerative injuries. The comparative results of the insole performance during jumping tests are shown in Table 2. The type A insole (35.6% attenuation) absorbed the shocks nearly three times as much as the type C insole (12.8% attenuation) during the jumping down test. The percent attenuation values shown in Table 2 reflect the average of the four subjects tested. The insoles were generally more effective in jumping down than in jumping in place. Here, as with the stair walking tests, the insoles were more effective in the reduction of the heel strike impacts than for the reduction for the metatarsal strike impacts. Statistical analyses (student's t-test) of the results presented in Tables 1 and 2 show that the shock attenuational capacity of the insoles type B and D were not significantly different in the four types of motion analysed (P> 0.01). Thus, the capacity of the insoles under investigation to attenuate shock can be ranked as best for type A, next for types B and D and, finally, for type C. The only exception to this ranking was the case of jumping in place; here the differences in the shock attenuation capacity for insoles A, B, and D were not significant
Summary and conclusions
The methodology described in this study was successfully used for a non-invasive, in-vivo evaluation of the impulsive shocks generated in the musculoskeletal system during various modes of human locomotion (i.e. stair climbing and jumping). The proposed technique of Table 2. Attenuational shock capacity of viscoelastic insoles during jumping
Insole type w/o A B C D
Insole type w/o A B C D
Jumping; in place Metatarsal strike (mean±s.D.) in g units
Number of trials
Subject no. 1
Subject no. 2
Subject no. 3
38 38 38 38 38
19.57 + 2.94 14.93 ±2.28 15.75 + 2.66 17.82 + 3.39 15.95±2.27
24.37 + 4.21 19.46 + 3.62 20.63 ±2.84 22.53±2.38 20.89 ±3.06
20.97 + 2.71 15.86 + 2.36 16.75+1.92 18.77 + 2.14 16.81 ±2.07
Jumping down Heel strike (mean±s.D.) in g units
. Percent Subject no. 4 attenuation 17.83±2.12 13.10+1.51 13.71 ±1.48 16.28 ±1.78 14.05 ±1.64
N.A. 23.69 ±2.65 19.52 + 3.19 8.92+1.21 18.46 ±2.99
Number of trials
Subject no. 1
Subject no. 2
Subject no. 3
. Percent Subject no. 4 attenuation
25 25 25 25 25
23.54 ±3.30 15.15 + 2.72 17.23 ±3.08 20.44 ±3.68 18.15+2.57
26.09 + 3.94 17.67±1.85 19.92±2.16 23.20+2.02 20.69 ±2.72
24.19 + 3.62 15.36+2.08 17.44 ±2.34 21.21+2.07 18.72 + 2.55
21.69±3.19 13.43 ±1.76 15.58 ±1.90 18.54±2.17 16.33 + 1.73
N.A. 35.62±2.45 26.63 ±2.07 12.77 + 1.44 22.73 ±1.64
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acquiring accurate bone acceleration data is sensitive enough to reveal differences in the shock absorbing properties of various shoes and insoles during stair walking and jumping. The main advantage of the technique presented is the use of the actual foot-shoe interaction during the evaluation. The same approach can be implemented during the development of new insoles and shock absorbing devices for specific applications in various modes of human locomotion. Stair walking and jumping had body motions different to walking, especially during the support phase. The support phases during both jumping cases and during walking down stairs were in the reverse sequence (metatarsal strike followed by the heel strike) of what is traditionally observed during level gait (heel strike followed by the metatarsal strike). The amplitudes of the shock waves induced by metatarsal strike were compatible to the ones resulting from the heel strike. The magnitudes of acceleration recorded during jumping and stair walking were significantly larger than that of the level gait. The biomechanical motion during walking up stairs is even more drastically different than other forms of locomotion since only a metatarsal strike exists. No heel strike is observed in walking up stairs since the heel of the foot never makes contact with the stair when going up the staircase. Stair walking in general may have a higher risk of degenerative damage occurring than walking on a level surface because of the larger magnitude of impact strikes during stair climbing. Jumping may be even more potentially damaging than either level gait or stair walking since the observed impact strikes were substantially larger in magnitude. Finally, viscoelastic insoles were very effective in modifying and absorbing the damaging impulsive shocks generated during stair walking and jumping. The insoles were more effective in the reduction of the heel strike impacts than in reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping cases than in the stair walking studies. References Clancy, W.G. (1980) Runner's injuries. Part Two. Evaluation and treatment of specific injuries. American Journal of Sports Medicine, 8, 287-9. Dekel, S. and Weissman, S.L. (1978) Joint changes after overuse and peak overloading of rabbit knees in vivo. Acta Orthopaedica Scandinavica, 49, 519-28. Folman, Y., Wosk, J., Voloshin, A. and Liberty, S. (1986) Cyclic impacts on heel strike: A possible biomechanical factor in the etiology of degenerative disease of the human locomotor system. Archives of Orthopaedic and Traumatic Surgery, 104, 363-5. Freeman, M.A.R. (1975) The fatigue of cartilage in the pathogenesis of osteoarthritis. Acta Orthopaedica Scandinavica, 46, 323-8. James, S.L., Bates, B.T. and Osternig, L.R. (1978) Injuries to runners. American Journal of Sports Medicine, 6, 40-50. Light, L.H., McLellan, G.E. and Klenerman, L. (1980) Skeletal transients on heel strike in normal walking with different footwear. Journal of Biomechanics, 13, 477-80. Lloyd-Smith, R., Clement, D.B., McKenzie, D.C. and Taunton, J.E. (1985) A survey of overuse and traumatic hip and pelvic injuries in athletes. The Physician and Sportsmedicine, 13, 131-41. Loy, D.J. (1987) The biomechanical evaluation of various modes of human locomotion. MS Thesis, Lehigh University. Miller, B.P. and Power, S.D. (1981) Developing power in athletes through the process of depth jumping. Track and Field Quarterly Review, 81, 52-4. Radin, E.L., Paul, I.L. and Rose, R.M. (1972) Role of mechanical factors in pathogenesis of primary osteoarthritis. The Lancet, 1, 519.
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Radin, E. L., Ehrlich, M.G., Charnack, R., Abernathy, P.J. and Paul, J.L. (1978) Effect of repetitive impulsive loading on the knee joints in rabbits. Clinical Orthopaedics and Related Research, 131, 288-93. Simon, S.R., Radin, E.L. and Paul, J.L. (1972) The response of joints to impact loading. II. In-vivo behavior of subchondral bone. Journal of Biomechanics, 5, 267. Simon, S.R., Paul, I.L., Mansour, J., Munro, M., Abernathy, P.J. and Radin, E.L. (1981) Peak dynamic force in human gait. Journal of Biomechanics, 14, 817-22. Stanish, W.D. (1977) Overuse injuries in runners. American Journal of Sports Medicine, 5, 40-50. Steben, R.E. and Steben, A.H. (1981) The validity of the stretch-shortening cycle in selected jumping events. Journal of Sports Medicine and Physical Fitness, 21, 28-37. Voloshin, A.S. (1988) Shock absorption during running and walking. Journal of the American Podiatric Medical Association, 78, 295-99. Voloshin, A.S. and Simkin, A. (1989) Evaluation of the skin-mounted versus bone-mounted accelerometer. Proceedings of the V Mediterranean Conference on Biomedical and Biological Engineering, MEDICON 89, 29 August-1 September, University of Patras, Patras, Greece, pp. 32-3. Voloshin, A.S. and Wosk, J. (1981) Influence of artificial shock absorbers on human gait. Clinical Orthopaedics and Related Research, 160, 52-6. Voloshin, A.S. and Wosk, J. (1982) In-vivo study of low back pain and shock absorption in human Iocomotor system. Journal of Biomechanics, 15, 21-7. Voloshin, A.S., Wosk, J. and Brull, M. (1981) Force wave transmission through human locomotor system. Journal of Biomechanical Engineering, 103, 48-50. Wosk, J. and Voloshin, A.S. (1981) Wave attenuation in skeletons of young healthy persons. Journal of Biomechanics, 14, 261. Ziegert, J.C. and Lewis, J.L. (1979) The effect of soft tissue on measurements of vibrational bone motion by skin-mounted accelerometers. Journal of Biomechanical Engineering, 101, 218-20.
Journal of Sports Sciences Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/rjsp20
Biomechanics of stair walking and jumping a
David J. Loy & Arkady S. Voloshin
a b
a
Department of Mechanical Engineering and Mechanics and Institute for Biomedical Engineering and Mathematical Biology , Lehigh University , Bethlehem, PA, 18015, USA b
Department of Mechanical Engineering and Mechanics , Lehigh University , 354 Packard Lab No. 19, Bethlehem, PA, 18015, USA Published online: 14 Nov 2007.
To cite this article: David J. Loy & Arkady S. Voloshin (1991) Biomechanics of stair walking and jumping, Journal of Sports Sciences, 9:2, 137-149, DOI: 10.1080/02640419108729875 To link to this article: http://dx.doi.org/10.1080/02640419108729875
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Journal of Sports Sciences, 1991, 9, 137-149
Biomechanics of stair walking and jumping DAVID J. LOY and ARKADY S. VOLOSHIN* Department of Mechanical Engineering and Mechanics and Institute for Biomedical Engineering and Mathematical Biology, Lehigh University, Bethlehem, PA 18015, USA
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Accepted 12 December 1989
Abstract
Physical activities such as stair walking and jumping result in increased dynamic loading on the human musculoskeletal system. Use of light weight, externally attached accelerometers allows for in-vivo monitoring of the shock waves invading the human musculoskeletal system during those activities. Shock waves were measured in four subjects performing stair walking up and down, jumping in place and jumping off a fixed elevation. The results obtained show that walking down a staircase induced shock waves with amplitude of 130% of that observed in walking up stairs and 250% of the shock waves experienced in level gait. The jumping test revealed levels of the shock waves nearly eight times higher than that in level walking. It was also shown that the shock waves invading the human musculoskeletal system may be generated not only by the heel strike, but also by the metatarsal strike. To moderate the risk of degenerative joint disorders four types of viscoelastic insoles were utilized to reduce the impact generated shock waves. The insoles investigated were able to reduce the amplitude of the shock wave by between 9% and 41% depending on the insole type and particular physical activity. The insoles were more effective in the reduction of the heel strike impacts than in the reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping trials than in the stair walking studies. The insoles were ranked in three groups on the basis of their shock absorbing capacity. Keywords: Shock absorption, jumping, stair climbing, viscoelastic insoles, dynamic loading, accelerometry.
Introduction
The human's environment is constantly changing from that of the natural grounds of the countryside to that of the concrete and asphalt reality of the modern industrial city. Another change encountered by the human in modern life styles is climbing up and down staircases, especially in office buildings. These alterations of the surroundings and fitness habits have resulted in much higher physical loads on the human musculoskeletal system even during normal everyday activities (Simon et al., 1972; Wosk and Voloshin, 1981). A recent comparative study showed that running on an asphalt surface generated shock *Send all correspondence to: Professor Arkady Voloshin, 354 Packard Lab No. 19, Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015, USA. 0264-0414/91 $03.00 + .12 © 1991 E. & F.N. Spon Ltd.
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waves with 40% higher amplitude than running on a grass surface (Loy, 1987). Several authors (Miller and Power, 1981; Steben and Steben, 1981) recommend drop jumping as an effective exercise for athletes who prepare themselves for explosive activities, such as sprinting and jumping. The impulsive loads to which the foot is subjected during any of those activities may be considerably higher than the individual's body weight, depending on gait velocity, degree of jumping and viscoelastic properties of the foot (Stanish, 1977). Because of these higher dynamic forces, the natural shock absorbers of the human musculoskeletal system may become insufficient. The impulsive energy which invades the body during each heel strike can no longer be sufficiently attenuated, modified and dissipated by the body's shock absorbers. This tends to an overloading of the natural shock absorbers of the human musculoskeletal system (Light et ah, 1980; Simon et ai, 1981; Voloshin and Wosk, 1982). The natural shock-absorbing structures in the musculoskeletal system are characterized by a viscoelastic time-dependent mechanical behaviour, which may become ineffective in withstanding sudden impulsive loads (Folman et ah, 1986; Radin et al., 1972). Degenerative joint diseases may thus be seen as a late clinical result of fatigue failure of the natural shock absorbers, submitted to the intermittent impacts over a period of time (Radin et al, 1972). Walking, running, and jumping are the common daily activities which introduce impacts of this nature into the locomotor system. Previous research has clearly shown a correlation between the cyclic impact loading on the absorbing joints and the degenerative process in their tissues (Dekel and Weissman, 1978; Radin et al., 1978). Even under normal physiological conditions, the intermittent and continuously repetitive onslaught of shock waves invading the locomotor system during gait tends to cause a slowly progressive weakening of the natural shock absorbers and may lead to headaches, lower back pain, degenerative joint disorders, and even osteoarthritis (Folman et al, 1986; Freeman, 1975; Voloshin and Wosk, 1982). Obviously, the higher impulsive cyclic loads generated during jumping and stair climbing will contribute to the progression of this degenerative process. Other related injuries stemming from sports utilizing jumping motions tend to occur in the hip and pelvic regions of the human musculoskeletal system (Clancy, 1980). These injuries were focused upon by a previous study which was retrospectively assessed at a general sports medicine clinic over a 2-year period (Lloyd-Smith et al., 1985). The three most common bone injuries were sacroiliitis, pelvic and femoral neck stress fractures, and osteitis pubis. The three most common soft-tissue injuries were gluteus médius strain/tendinitis, trochanteric bursitis and hamstring strain (Clancy, 1980; James et al., 1978; Lloyd-Smith et ah, 1985). Overuse accounted for 82.4% of the injuries recorded which were most commonly a result of the higher than normal impulsive loads experienced from running, fitness classes and racquet sports. The treatment of these individuals generally consisted of modified activity, local muscle rehabilitation, heel lifts and/or viscoelastic insoles, change of footwear, and a gradual reintroduction of the specific physical activity. Obviously, the significant reduction or even elimination of the injurious effects of the shock waves are contingent upon the development of accurate methods to quantify these waves and the effect of various shock absorbing insoles on the human body. The results from previous studies showed that the use. of viscoelastic insoles during normal walking can decrease the amplitude of the shock wave propagating through the body and, therefore protect the joints from overloading their capacity to sustain intermittent loading (Light et ah, 1980; Voloshin and Wosk, 1981). The main aim of this study was to use a non-invasive methodology in vivo to evaluate the impulsive loads experienced by the human musculoskeletal system during normal jumping and stair climbing. An evaluation of the
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shock absorbing capacity of different insoles during those physical activities was also performed.
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Methodology This investigation utilized a novel approach, by which a small low-mass PCB piezoelectric accelerometer was placed on the skin surface of the tibial tuberosity (Voloshin et al, 1981). The accelerometer was externally fixed to the human subject with adhesive tape and a tightly wrapped elastic bandage in order to provide measurements as close as possible to an actual bone acceleration during stair walking and jumping. Such attachment of the accelerometer caused the natural frequency of the recording instrumentational set-up to exceed that observed in stair walking and jumping, thus avoiding error due to resonance (Ziegert and Lewis, 1979; Loy, 1987). Comparison of the acceleration amplitude measured by a skinmounted accelerometer to the one rigidly attached to the bone by screws showed differences below 5%. Those experiments were performed in vitro on a fresh cadaver's leg subjected to a simulated loading representing heel strike (Voloshin and Simkin, 1989). The signal was acquired by a TEAC MR-30 multi-channel analogue data cassette recorder and play back unit, with a frequency bandwidth of DC to 1250 Hz. The input was simultaneously monitored with a digital oscilloscope (BK Precision Model 2520, Dynascan Corp.). The signal from the accelerometer was low-pass filtered with the cut-off frequency of 120 Hz. These tapes were then digitized using a personal computer (Zenith 158) modified into a high-speed multi-channel data acquisition and storage system. A Metrabyte Dash-16 (12 bit resolution) A-D converter was utilized to quantify the analogue data prior to recording into data files. The sampling rate was 1000 Hz, ensuring an accurate representation of the filtered signal. Four males in their early 20s (range 20 to 22 years) served as test subjects for both parts of this study. After recording the subject information, each individual was allowed 20 to 40 min to get used to walking naturally up and down the test staircase while connected to the recording instrumentation. At this time, the cable connections, accelerometer placements, and their responses were checked. Each subject then walked four trials up the staircase, all subjects using the same pair of hard heel test shoes (without insole). Most trials usually generated between eight and nine steps of recorded data. This was then followed by four trials of walking up the staircase for each particular pair of viscoelastic insoles to be tested. Afterwards, the same procedure was then repeated for the trials which entailed walking down the staircase. In the next part of the study the impact acceleration data from the tibial tuberosity was acquired using the same subjects and instrumentation during jumping. Each subject jumped up and down in place to generate 30 to 40 sets of data while using the same pair of test sneaker (no-brand name tennis shoe) without insole. This was followed by 30 to 40 trials of jumping in place for each of the same set of viscoelastic insoles tested during the stair walking portion of this study. The subjects were trained to jump repetitively and consistently to the same height above the ground each time (approximately 0.3 m). It was also very important to have the subjects jump and land with as similar a motion as possible. Moreover, any trial that was subjectively determined to be inconsistent with the general trend was discarded and repeated. After the study of jumping in place was completed, the impact of landing was investigated further by having each subject jump naturally from a standing position off a chair platform
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approximately 0.4 m above the ground. The shock absorbing capacity of the same set of viscoelastic insoles was also tested and evaluated for jumping down. Four types of viscoelastic insoles were utilized in this study to reduce the impact shocks generated during stair walking and jumping tests. The insoles A and B were thick composite type insoles contoured to the bottom of the foot and contained portions of viscoelastic material embedded into the urethane foam construction. The type A insole had the viscoelastic material both under the heel (8 mm thick) and metatarsal area (4.5 mm thick) of the insole, while the type B insole had the viscoelastic material under the heel only (6.5 mm thick). The insoles type C and D were of a less complex design. The type C insole was of a plane, thin design, except for the heel (6 mm thick). The insole was constructed entirely of viscoelastic material. The type D design was similar to that of the type A composite insole, with viscoelastic material located under the heel (6.5 mm thick) and metatarsal regions (3.5 mm thick). However, the grooved indentations in these viscoelastic portions of the insole were relatively small. The footwear and insoles were consistently fitted prior to data collection. All subjects used the same footwear and the same set of insoles. The order of the viscoelastic insoles being tested was randomly changed for each subject. The jumping portion of this study took place in a corridor with the floor consisting of poured concrete covered with floor tiles. In the stair walking case, the walking length of each trial was a climb of nine stair steps resulting in a total elevational rise of 1.7 m. The subjects' average gait velocities during these tests were adjusted to approximately 0.91 step s" 1 going up stairs and 1.1 step s" 1 heading down stairs.
Results and Discussion Stair walking The acceleration data recorded while stair walking showed differences in the gait pattern motions between those experienced while walking up or down a staircase and that of walking on level ground. A typical accelerogram recorded from the tibial tuberosity of a subject walking on level ground wearing hard heel test shoes (without insoles) is presented in Fig. 1. The subject's walking style was similar to the patterns observed in the previous level ground gait studies (Loy, 1987; Voloshin, 1988). The usual sequence of events observed in a level gait pattern proceeds with the large steep heel strike (approximately 3.0 g in this case) followed closely by a small positive double peak bulge (usually 0.1 s after heel strike) containing the insignificant metatarsal strike and push-off. Another feature observed in this type of gait pattern, is that of the acceleration resulting from the toe-off of the leg. This event occurs at about half the time between successive heel strikes (approximately 0.5 s after heel strike). In contrast, the gait pattern recorded for walking up a staircase does not have heel strike present as is the case with level ground gait. The heel of the foot never makes contact with the stair when going up the staircase. The biomechanics of the gait motion while walking up stairs is different because only the metatarsal part of the foot makes contact with the ground (stair) during each step. In addition, there is usually little space on the step to place a whole foot. Those metatarsal strikes, as seen at 0.25 and 1.25 s in Fig. 2a, are of higher magnitude (approximately 5.9 g) and less slope than that of the heel strike experienced during normal gait on level ground. The impulsive loads experienced in climbing stairs at roughly the same gait velocity were over 180% of that observed for level gait. It is interesting that there was no
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LEFT TIBIA RESPONSE DURING GAIT »/o INSOLE
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3.00..
-2.00..
-3.001
Fig. 1. Accelerogram of a level gait observed at the subject's left tibial tuberosity. reaction from the opposing leg's impact seen in the accelerogram for walking up stairs. This seems puzzling since the strike magnitudes are so much greater than that experienced on level ground. Even though it may take more studies to determine the reasoning for this occurrence, the unorthodox leaning positioning experienced by the human body during stair climbing and the bend at the knee joint are strongly suspected as the cause. The gait pattern observed for walking down stairs (Fig. 2b) does show a similar opposing heel strike reaction phenomenon as previously observed in the level gait pattern. Even so, the biomechanics of walking down stairs is significantly different from that observed for normal gait on level ground or climbing up stairs. The metatarsal of the foot makes the first contact with the stair during walking down stairs as was the case in walking up a staircase. However, the metatarsal strike does not usually generate the same impulsive magnitudes seen during gait going up stairs. Even though the metatarsals touch the stair first, the body is not brought to a complete stop on that step until the heel strike impact occurs. This can be clearly seen in the accelerogram for walking down a staircase (Fig. 2b). The heel strikes of approximately 7.8 g occur at 0.25 s and 1.15 s and are preceded by a couple of small positive peaks (around 1.0 g) resulting from the action generated by the metatarsal contact during this portion of the support phase. Moreover, the impact strike magnitudes generated during walking down a staircase were nearly 130% greater than that observed in walking up stairs and 250% greater than that experienced in normal level gait (Loy, 1987), as shown in Fig. 3. This indicates that the physical action of walking down stairs results in higher dynamic loads on the human musculoskeletal system than that of walking up stairs and even more so than walking on level ground. To moderate the increased dynamic load on the human musculoskeletal system, four different types of viscoelastic insoles were utilized to reduce the impact shocks generated during stair walking. The acceleration amplitudes measured at the tibial tuberosity (Table 1) indicated overall reduction of the dynamic loading on the human musculoskeletal system while using in-shoe viscoelastic insoles. In the most extreme case, the type A insole was nearly
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7.5 _
WALKING UP A STAIRCASE t/t INSOLE
Time (S ) WALKING DOWN A STAIRCASE n/o INSOLE
1.5
Ti me CS; 1 -5.9 1 Fig. 2. Acceleration pattern recorded at the left tibial tuberosity of a subject walking (a) up and (b) down a staircase.
three times more shock-absorbing than the type C insole for either type of stair walking. The designed moulded grooves present in the viscoelastic portions allowed the viscoelastic material to flow more freely when worn in the constrictions of the shoe, thus giving the insole better damping properties (Table 1). The percent attenuation values shown in Table 1 reflect the average value for the four subjects tested. The percent attenuations were calculated from the mean metatarsal strike values for the up stairs trial and from the mean heel strike values for the down stairs trial. The 'without insole' values were used as the basis in both cases. Even though the insoles tested in this study significantly reduced the impact shocks in both stair gait types, it is quite clear that the insoles were more shock absorbing in walking down stairs
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Acceleration (g)
8 -
m
6
H
S
walking up
walking down
4
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level gait
Fig. 3. Acceleration values in level walking and stair climbing.
Table 1. Attenuational shock capacity of viscoelastic insoles in stair walking Insole type w/o A B C D
Insole type w/o A B C D
Walking up a staircase Metatarsal strike (mean + s.D.) in g iinits
Number of trials
Subject no. 1
Subject no. 2
34 34 34 34 34
5.45 + 0.42 3.98 ±0.38 4.24 + 0.39 4.94 + 0.43 4.36+0.41
6.49 ±0.71 4.66 + 0.56 4.91 ±0.47 5.75 ±0.60 4.98 + 0.54
Number of trials 34 34 34 34 34
Percent Subject no. 3 Subject no. 4 attenuation 6.13 + 0.63 4.42 + 0.56 4.75 + 0.46 5.53+0.62 4.83 + 0.53
5.16±0.49 N.A. 3.86+0.43 27.06 ±1.36 4.12±0.37 22.30+1.71 4.71 ±0.51 9.86+1.22 4.15±0.48 21.01 ±1.66
Walking down a staircase Heel strike (mean + s.D.) in g units Subject no. 1 Subject no. 2 7.83 ±0.67 4.60 ±0.42 5.43 ±0.49 6.65±0.51 5.76 ±0.53
8.70 ±0.93 4.85 ±0.54 5.80+1.20 7.14 ±1.48 6.22 ±0.94
Percent Subject no. 3 Subject no. 4 attenuation 6.58+0.73 3.73+0.91 4.48 + 0.57 5.51+0.67 4.89 + 0.38
7.00 ±0.94 4.33 ±0.68 5.04±0.69 5.65 ±0.99 4.96±0.53
N.A. 41.73 ±2.72 30.96 ±2.28 17.14+1.85 27.44 ±1.65
than in walking up stairs. This was not that surprising since the insole designs were mainly focused upon the reduction of the well known heel strike rather than that of the newly recognized metatarsal strike. Also, these modifications of the impact shocks can be clearly seen by comparing the recorded stair gait accelerograms of both the 'with insole' (Figs 4a and 4b) and 'without insole' cases (Figs 2a and 2b). Jumping The next phase of this work dealt with the biomechanical aspects of jumping. The same set of viscoelastic insoles as utilized in the stair walking was tested in both types of jumping.
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7.5 ,.
-2. S l 10. 0 _
WALKING UP A STAIRCASE
Time CS 1 WALKING DOWN A STAIRCASE
Time (S ) -5.0 1 Fig. 4. Acceleration signal recorded at the left tibial tuberosity of a subject walking (a) up and (b) down a staircase using type A insoles. The accelerograms of signals recorded from the tibial tuberosity of the subject while jumping in place wearing test sneakers with and without viscoelastic insoles are shown in Figs 5b and 5a respectively. The jumping patterns are essentially the same except for the significant reduction in impulsive strike magnitudes by an insole. There are two sets of impulsive strikes observed in the accelerograms for jumping in place. The first set of these impulsive strikes was associated with the landing phase. It can be seen clearly as the leading sets of uneven double spikes (first peak - 20.0 g, second peak - 15.5 g) occurring at 0.25 and 0.85 s (Fig. 5a). The second set of impulsive strikes, located at 0.35 and 1.0 s (Fig. 5a), was associated with the push-off motions for the next successive jump.
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Biomechanics of stair walking and jumping 25
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TIBIA RESPONSE TO JUMPING IN PLACE
(a)
15.0 .
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-5.0 ..
Time IS I -15.0
2S
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TIBIA RESPONSE TO JUMPING IN PLACE
(b)
15.0 ..
5.0 ..
a a a
—»
1.5
-5.0 ..
Time IS ! -IS.O 1 Fig. 5. Acceleration pattern recorded on the tibial tuberosity of a subject jumping in place (a) without insoles and (b) with insoles.
The landing phase observed in the accelerograms for jumping in place usually contained two peaks. The first peak was the metatarsal strike followed closely (approximately 50 ms) by the heel strike. This is the reverse order of strikes observed in level walking patterns. The impact magnitudes of these peaks vary according to the way an individual lands on his feet. One who lands mostly on the metatarsal and less on the heel of the foot would have a higher first peak followed by a significantly smaller second peak. Alternatively, one who lands lightly on the metatarsal and more on the heel of the foot would have a smaller first peak followed by a higher second peak. Thus, depending on the individual landing pattern, there is a countless combination of double strike values possible for jumping in place.
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While the landing phase of jumping in place had two distinct peaks, the landing in the jumping down usually only had one major peak which was clearly associated with the heel strike. This can be seen in the accelerograms recorded for jumping down (Figs 6a and 6b). An interesting observation seen for both the stair walking and jumping studies was that an individual tended to land more with the metatarsal of the foot when needing a propelling forward push-off for the next successive step or jump (as with jumping in place and walking up stairs), and more with the heel of the foot when coming to a more complete stop on the
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25.0 „
TIBIA RESPONSE TO JUMPING DOWN
(a)
_
15.0 .
o> c o
—
5.0
.,
1.5
-5.0 .. o
-15.0 ..
Time (S )
-25.0 1 25.0 ,.
TIBIA RESPONSE TO JUMPING DOWN
(b)
_
15.0 ..
c a
—
5.0
1.0
S -5.0
-15.0 ..
1.5
Time IS 1
-25.0 1
Fig. 6. Acceleration pattern recorded on the tibial tuberosity of a subject jumping down (a) without insole and (b) with insole.
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ground or steps (as with jumping down and walking down stairs). The strike magnitudes of either type of jumping are five to ten times greater than those experienced during level gait. Thus, the individuals who avidly participate in sport activities which contain significant amounts of jumping (i.e. basketball, aerobics and so on) may expose their musculoskeletal system to accelerated risk of degenerative injuries. The comparative results of the insole performance during jumping tests are shown in Table 2. The type A insole (35.6% attenuation) absorbed the shocks nearly three times as much as the type C insole (12.8% attenuation) during the jumping down test. The percent attenuation values shown in Table 2 reflect the average of the four subjects tested. The insoles were generally more effective in jumping down than in jumping in place. Here, as with the stair walking tests, the insoles were more effective in the reduction of the heel strike impacts than for the reduction for the metatarsal strike impacts. Statistical analyses (student's t-test) of the results presented in Tables 1 and 2 show that the shock attenuational capacity of the insoles type B and D were not significantly different in the four types of motion analysed (P> 0.01). Thus, the capacity of the insoles under investigation to attenuate shock can be ranked as best for type A, next for types B and D and, finally, for type C. The only exception to this ranking was the case of jumping in place; here the differences in the shock attenuation capacity for insoles A, B, and D were not significant
Summary and conclusions
The methodology described in this study was successfully used for a non-invasive, in-vivo evaluation of the impulsive shocks generated in the musculoskeletal system during various modes of human locomotion (i.e. stair climbing and jumping). The proposed technique of Table 2. Attenuational shock capacity of viscoelastic insoles during jumping
Insole type w/o A B C D
Insole type w/o A B C D
Jumping; in place Metatarsal strike (mean±s.D.) in g units
Number of trials
Subject no. 1
Subject no. 2
Subject no. 3
38 38 38 38 38
19.57 + 2.94 14.93 ±2.28 15.75 + 2.66 17.82 + 3.39 15.95±2.27
24.37 + 4.21 19.46 + 3.62 20.63 ±2.84 22.53±2.38 20.89 ±3.06
20.97 + 2.71 15.86 + 2.36 16.75+1.92 18.77 + 2.14 16.81 ±2.07
Jumping down Heel strike (mean±s.D.) in g units
. Percent Subject no. 4 attenuation 17.83±2.12 13.10+1.51 13.71 ±1.48 16.28 ±1.78 14.05 ±1.64
N.A. 23.69 ±2.65 19.52 + 3.19 8.92+1.21 18.46 ±2.99
Number of trials
Subject no. 1
Subject no. 2
Subject no. 3
. Percent Subject no. 4 attenuation
25 25 25 25 25
23.54 ±3.30 15.15 + 2.72 17.23 ±3.08 20.44 ±3.68 18.15+2.57
26.09 + 3.94 17.67±1.85 19.92±2.16 23.20+2.02 20.69 ±2.72
24.19 + 3.62 15.36+2.08 17.44 ±2.34 21.21+2.07 18.72 + 2.55
21.69±3.19 13.43 ±1.76 15.58 ±1.90 18.54±2.17 16.33 + 1.73
N.A. 35.62±2.45 26.63 ±2.07 12.77 + 1.44 22.73 ±1.64
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acquiring accurate bone acceleration data is sensitive enough to reveal differences in the shock absorbing properties of various shoes and insoles during stair walking and jumping. The main advantage of the technique presented is the use of the actual foot-shoe interaction during the evaluation. The same approach can be implemented during the development of new insoles and shock absorbing devices for specific applications in various modes of human locomotion. Stair walking and jumping had body motions different to walking, especially during the support phase. The support phases during both jumping cases and during walking down stairs were in the reverse sequence (metatarsal strike followed by the heel strike) of what is traditionally observed during level gait (heel strike followed by the metatarsal strike). The amplitudes of the shock waves induced by metatarsal strike were compatible to the ones resulting from the heel strike. The magnitudes of acceleration recorded during jumping and stair walking were significantly larger than that of the level gait. The biomechanical motion during walking up stairs is even more drastically different than other forms of locomotion since only a metatarsal strike exists. No heel strike is observed in walking up stairs since the heel of the foot never makes contact with the stair when going up the staircase. Stair walking in general may have a higher risk of degenerative damage occurring than walking on a level surface because of the larger magnitude of impact strikes during stair climbing. Jumping may be even more potentially damaging than either level gait or stair walking since the observed impact strikes were substantially larger in magnitude. Finally, viscoelastic insoles were very effective in modifying and absorbing the damaging impulsive shocks generated during stair walking and jumping. The insoles were more effective in the reduction of the heel strike impacts than in reduction of the metatarsal strike impacts. In all instances, the shock attenuation capacities of the insoles tested were greater in the jumping cases than in the stair walking studies. References Clancy, W.G. (1980) Runner's injuries. Part Two. Evaluation and treatment of specific injuries. American Journal of Sports Medicine, 8, 287-9. Dekel, S. and Weissman, S.L. (1978) Joint changes after overuse and peak overloading of rabbit knees in vivo. Acta Orthopaedica Scandinavica, 49, 519-28. Folman, Y., Wosk, J., Voloshin, A. and Liberty, S. (1986) Cyclic impacts on heel strike: A possible biomechanical factor in the etiology of degenerative disease of the human locomotor system. Archives of Orthopaedic and Traumatic Surgery, 104, 363-5. Freeman, M.A.R. (1975) The fatigue of cartilage in the pathogenesis of osteoarthritis. Acta Orthopaedica Scandinavica, 46, 323-8. James, S.L., Bates, B.T. and Osternig, L.R. (1978) Injuries to runners. American Journal of Sports Medicine, 6, 40-50. Light, L.H., McLellan, G.E. and Klenerman, L. (1980) Skeletal transients on heel strike in normal walking with different footwear. Journal of Biomechanics, 13, 477-80. Lloyd-Smith, R., Clement, D.B., McKenzie, D.C. and Taunton, J.E. (1985) A survey of overuse and traumatic hip and pelvic injuries in athletes. The Physician and Sportsmedicine, 13, 131-41. Loy, D.J. (1987) The biomechanical evaluation of various modes of human locomotion. MS Thesis, Lehigh University. Miller, B.P. and Power, S.D. (1981) Developing power in athletes through the process of depth jumping. Track and Field Quarterly Review, 81, 52-4. Radin, E.L., Paul, I.L. and Rose, R.M. (1972) Role of mechanical factors in pathogenesis of primary osteoarthritis. The Lancet, 1, 519.
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