This article was downloaded by: [University of Saskatchewan Library] On: 30 January 2015, At: 06:49 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Downhill walking to improve lower limb strength in healthy young adults a
Angelo Rodio & Luigi Fattorini
b
a
Department of Human Sciences, Society and Health, University of Cassino e Southern Lazio, Cassino (FR), Italy b
Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Rome, Italy Published online: 23 Apr 2014.
Click for updates To cite this article: Angelo Rodio & Luigi Fattorini (2014) Downhill walking to improve lower limb strength in healthy young adults, European Journal of Sport Science, 14:8, 806-812, DOI: 10.1080/17461391.2014.908958 To link to this article: http://dx.doi.org/10.1080/17461391.2014.908958
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
European Journal of Sport Science, 2014 Vol. 14, No. 8, 806–812, http://dx.doi.org/10.1080/17461391.2014.908958
ORIGINAL ARTICLE
Downhill walking to improve lower limb strength in healthy young adults
ANGELO RODIO1 & LUIGI FATTORINI2 1
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
2
Department of Human Sciences, Society and Health, University of Cassino e Southern Lazio, Cassino (FR), Italy; Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Rome, Italy
Abstract Walking is the most natural physical activity to maintain and improve fitness and health. Walking downhill is usefully adopted to plan training programmes to improve the strength, particularly in older adults. The present research was aimed to evaluate the influence of downhill walking on leg strength in young adult. A total of 32 females (age 26 ± 4 years; height 1.64 ± 0.05 m; body mass 57.6 ± 5.6 kg) were divided into four groups and they carried out an exercise intervention consisting of three sessions per week for 6 weeks, each lasting 30 minutes. Groups were defined at several workloads characterised by treadmill inclination (%) and walking speed (m·s−1): Level Walking at treadmill inclination 0% and walking speed 1.0; Uphill Walking at +20%, 0.75; Downhill Walking (DW) at −20%, 1.36; and Mixed Walking at +20%, 0.75 and −20%, 1.36 each lasting 15 minutes. Maximum voluntary contraction (MVC) developed by the Quadriceps Femoris and Endurance Time at 60% MVC were evaluated before and after experimental period. At the end of each session, Borg’s scale and Visual Analogue Scale (VAS) were adopted in order to evaluate perception of rate exertion and pain. Statistical analysis showed significant only in MVC for DW in both right and left legs. Borg’s scale and VAS described light activity free of pain. Present findings showed how an eccentric exercise, short lasting and at a low workload, can be useful in inducing improvements in leg strength. Keywords: Sedentary, eccentric training, workload, slope, optimal speed
Introduction Physical inactivity is a specific condition largely diffuse within populations of industrial countries. Sedentary lifestyles, as a consequence of physical inactivity, are to be found in every age from childhood to the elderly in both genders. Sedentariness increases all causes of mortality, the risk of cardiovascular diseases and obesity, as well as the risk of colon cancer, high blood pressure, depression and anxiety. According to Bonow, Smaha, Smith, Mensah, and Lenfant (2002) on the basis of the WHO report, 60–85% of people in the world—from both developed and developing countries—lead sedentary lifestyles, making it one of the most serious public health problems. Recently, Campbell et al. (2013) have shown in young adults lower levels of force values in comparison to the norm owing to sedentary habits. But, low strength values, just in the younger, over time could induce an aggravation
of physiological decay (Grimby & Saltin, 1986; Haskell et al., 2007; Lindle et al., 1997). It has been proved that eccentric muscle contraction is a valid form of physical exercise able to cause increases in maximal force by inducing hypertrophy of type II muscle cells (Fridèn, Seger, Sjostrom, & Ekblom, 1983; Fridèn, 1984; Roig et al., 2009). Eccentric contractions (ECCs) are muscular activations requiring force generation during lengthening, typically occurring when a muscle opposes a stronger force, which causes the muscle to lengthen as it contracts. Several daily activities bring into play an ECC such as going downstairs, walking or running downhill, lowering weights, the downward motion of squats and push-ups/pull-ups. Several training protocols have been proposed to increase absolute force using ECCs (Marcus, LaStayo, Dibble, Hill, & McClain, 2009) whereas, in the same context, the present paper explores the possibility of using walking downhill as a training
Correspondence: Luigi Fattorini, Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Piazz.le Aldo Moro, 5, 00185 Rome, Italy. E-mail: [email protected] © 2014 European College of Sport Science
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
Downhill walking and lower limb strength tool. In fact, walking on negative slopes requires the nervous system to define contemporarily and in parallel two complex motor tasks: gait and balance. On negative slopes, the centre of mass is in front of the sagittal plane and, in steady stance, muscular activation must be present to counteract loss of stability in particular on leg and trunk muscles (among others quadriceps femori, adductor longus, adductor magnus, gluteus maximus, trapezius and latissimus). Moreover, walking is considered an effective physical activity for the maintenance and improvement of aerobic fitness (Haskell et al., 2007), for the prevention of cardiovascular and metabolic diseases, as reported by the American College Sports Medicine guidelines, and it may also be performed as a pleasant natural outdoor activity (American College of Sports Medicine [ACSM], 2005; Fattorini et al., 2012; Williams, 2008). Recently, walking downhill has been proposed as physical activity to improve functional mobility and force in older adults (Gault, Clements, & Willems, 2012; Gault, & Willems, 2013). The treadmill slope concept as used by Gault et al. (2012) and Gault and Willems (2013) was set at –10% because this is the point at which minimum total body energy cost occurs for downhill walking (Ardigò, Saibene, & Minetti, 2003). Gault et al.’s (2012) findings showed as maximal isokinetic force on lower limbs was not modified after exercise intervention, whilst mobility capacity increased, which could be a reflection of improved balance and coordination but not of strength changes. In a previous paper, the same authors argued that similar experimental conditions induced a muscular injury (Gault, Clements, & Willems, 2011) because the maximal leg force decreased 48 hours after with respect to baseline and it is a well-known fact that muscle cell trauma is a typical procedure which increases muscular force (LaStayo, Pierotti, Pifer, Hoppeler, & Lindstedt, 2000; Lindstedt, LaStayo, & Reich, 2001). Finally, in a more recent paper, which assessed isometric maximal contractions, Gault and Willems (2013) obtained an increase of about 5% in leg force in healthy older adults. The present research was designed to propose a physical intervention in young adults in order to counteract a decrease in force due to physical inactivity in this population. It is a well-known fact that generally, above 60 years of age, a physiological decline in musculoskeletal function, balance and mobility can be seen (Nolan, Nitz, Low Choy, & Illing, 2010). Hence, it is credible to argue that in young subjects the workload must be higher than in older ones to obtain comparable functional changes. For this reason, authors chose to increase the physical intervention intensity with respect to Gault
807
and Willems (2013) by implementing a steeper downhill treadmill inclination. The aim of the present study was to assess shortterm changes in muscle strength in a healthy young population using a 6-week long exercise intervention consisting of walking downhill on a treadmill set at a −20% gradient for three sessions per week. Materials and methods Subjects A total of 32 young adult female students were enrolled for the study (age 26 ± 4 years; height 1.64 ± 0.05 m; body mass 57.6 ± 5.6 kg; body mass index 21.4 ± 1.8 kg m−2). All individuals referred a moderate level of physical activity, confirming that they had not been involved in any kind of systematic training for at least 6 months prior to the present study. Also during the experimental period subjects were asked to avoid any other form of physical activity. Exclusion criteria included major neurological disorders, major musculoskeletal diseases or recent musculoskeletal injuries and cardiovascular disease. All subjects signed an informed consent after reading a description and scope of the experimental protocol. Institutional ethics committee approval was received for all study procedures, and the study conformed to the provisions of the Declaration of Helsinki. Exercise intervention protocol A week before the exercise intervention programme onset, all subjects visited the lab in order to familiarise with all experimental procedures. They were invited to walk on the treadmill under three different conditions per inclination and speed, each lasting about 5 minutes: 0% at 1.0 m·s−1; +20% at 0.75 m·s−1; and −20% at 1.36 m·s−1. Once the exercise intervention protocol began, all subjects underwent three sessions per week for 6 weeks, each session lasting 30 minutes. Within this context, subjects were randomly divided into four groups, each assigned to one of the following walking conditions on the treadmill (Runrace, Technogym, Italy) based on inclination and speed: Level Walking (LW) 0% at 1.0 m·s−1; Uphill Walking (UW) +20% at 0.75 m·s−1; Downhill Walking (DW) −20% at 1.36 m·s−1; and Mixed Walking (MW) at +20%, 0.75 m·s−1and at −20%, 1.36 m·s−1 each lasting 15 minutes. Negative Treadmill slopes were obtained by means of a customised phase inverter in order to generate the motor revolution in reverse cycle. Each speed was chosen in order to minimise the walking energy cost at aforementioned inclinations in accordance with Ardigò et al. (2003).
808
A. Rodio & L. Fattorini
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
Measurements For each subject, measurements of body composition, lower limb exerted force and Endurance Time (ET) were carried out a week before and after the experimental protocol. Body composition was determined by body fat mass evaluation using the nine-skinfold method and was reported as a percentage of total body mass (Jackson, Pollock, & Ward, 1980). Maximum voluntary contraction (MVC) developed by the Quadriceps Femoris was evaluated. Three maximal contraction attempts, each separated by a 5-minute rest, were performed and the maximal force measured was taken as the MVC value. Quadriceps Femoris ET at 60% MVC in isometric conditions was carried out on both legs, as the fatigue index. Banister (1979) has proven that there is only a small difference between exertion perception at 60% MVC and maximum perception of the effort of which the individual thinks he is capable. It is evident that 60% MVC is easier to maintain than MVC in especially in a no skilled population, therefore 60% MVC was chosen. During MVC and ET tests, the subject was seated in a customised chair; the vertical plan of the chair was adjustable in rotation and translation to set hip and knee angles at 110° and 90°, respectively, and capable of adapting to the individual’s anthropometric parameters. The subject’s hips and shoulders were restrained with straps and the arms folded to avoid the possibility of other muscles being involved in the movement. After a period of familiarisation with the experimental apparatus, the subject was encouraged to develop the force as fast as possible. The subject wore a boot on the side being examined with a special orthesis that locked the ankle joint at 90° and a ring was placed on the rear side connecting the piezoelectric force transducer (type 9311A, Kistler, Switzerland) to the chair. Force signal was amplified with a charge amplifier (type 5006, Kistler, Switzerland) and stored via an A/D converter (ATMIO, 12 bit, sample frequency 2048, National Instruments, USA) on a desktop computer. Force values were expressed as kilograms. ET test at 60% MVC in isometric conditions was carried out after at least 30 minutes from the last maximal contraction performed. This consisted in maintaining as much as possible the target force level showed on a screen. ET was computed offline as the time period where subject’s force was maintained stable on target around an error of 10%. This test was performed in the same MVC set-up. At the end of each training session, all subjects filled out two reports in order to describe rate of perceived exertion and pain following a 6–20 Borg’s
scale (Borg, 1998) and a 0–10 cm Visual Analogue Scale (VAS; Noble et al., 2005). Leg dominancy In the present study, three standard tests were used to establish leg dominancy; these were all performed before the comprehensive experimental protocol. The tests consisted of the following procedures: .
.
.
The subject had to step onto a platform (40 cm), where the leading leg spontaneously chosen by the subject was considered to be the dominant leg; In a standing up position with feet parallel, subjects were pushed forcefully from behind between the shoulder blades and the leg with which they attempted to regain their balance was considered the dominant leg; Lastly, subjects were asked with which leg they kicked a ball. Here again, the chosen leg was considered to be dominant.
In the present study, the dominant leg was defined as the leg that was dominant in at least two of the three tests. To check for consistency, the step test and the balance recovery test were repeated in between the dynamometer tests on both legs and again at the end of the first session. Statistical analysis Statistical analysis was undertaken using StatView for Windows ver. 5.0.1 (SAS, Cary, NC, USA). All data are expressed as means and relative standard deviations. A two-way repeated measures analysis of variance (ANOVA) was used to examine the change from all time points and between all conditions for all parameters. If this analysis evidenced significant differences, a paired Student’s t-test (Bonferroni corrected) to compare the mean values of the measured parameters before and after training protocol was used. Moreover, statistical power and sample size was performed. Significant statistical level was set at p < 0.05. Results Table I shows subjects’ anthropometric characteristic data and fat mass percentage. As can be seen, subjects were divided into four groups according to relative walking tasks where no differences among groups were recognised by statistical analysis. During the experimental phase, four subjects left the exercise programme, of which two in MW group (mixed), one in LW (flat) and one in DW (downhill) due to personal and not experimental reasons.
809
Downhill walking and lower limb strength Table I. Subjects’ anthropometric characteristics on the four groups (data presented as mean and SD) Group
Age (years)
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
LW UW DW MW
26 27 24 24
± ± ± ±
Height (m)
6 4 3 4
1.62 1.62 1.64 1.69
± ± ± ±
Body mass (kg)
0.05 0.06 0.04 0.03
61.67 57.89 57.77 60.60
A prevalence of right-leg dominance was found for all four groups except in two subjects, belonging to MW and UW. In all groups, fat and body mass values before (Table I) and after the experimental programme were not statistically different (p > 0.05). Absolute force values were in a range between 190–390 N for right leg and 190–380 N for left leg; no statistical differences were recognised between legs and groups. Same measurements expressed as kilograms scaled by body mass, before and after exercise programme, are shown in Table II. ANOVA did not show differences between legs and groups at baseline, F(3, 28) = 2.461; p = 0.127, and after the intervention, F(3, 24) = 1.248; p = 0.314. In all groups, strength values were increased from baseline to post-intervention but resulted statistically different only in DW group for both legs (t(6) = 6.708; p < 0.001, and t(6) = 5.195; p < 0.001, in right and left legs, respectively). Also significant differences were obtained in MW, but the sample size in post-intervention, due to the drop out, did not guarantee the statistical power of the test so the Hypothesis 1 was rejected. ET values are shown in Table III. Here again, no statistical differences were to be seen between legs and groups. On the grounds of VAS tests carried out during the 18 sessions (total of 6 weeks), the perception of pain showed no change for LW (0%), MW and UW (20%). Whilst for DW (−20%) equivalent, VAS findings showed an increase in the perception of pain up to the third session where a peak value of 3 was to be seen, after which values already returned to Table II. Force values scaled by body mass before and after training Right leg (a.u.) Group LW UW DW MW
Before 0.44 0.51 0.47 0.41
*p < 0.05.
± ± ± ±
0.11 0.16 0.09 0.12
Left leg (a.u.)
After 0.51 0.58 0.57 0.49
± ± ± ±
0.14 0.13 0.09* 0.11
Before 0.45 0.51 0.45 0.40
± ± ± ±
0.11 0.13 0.06 0.06
After 0.51 0.56 0.57 0.51
± ± ± ±
0.12 0.18 0.11* 0.11
± ± ± ±
Body mass index (kg m−2)
7.34 6.86 5.28 5.13
23.55 22.06 21.52 21.14
± ± ± ±
Fat mass (%)
6.90 2.61 1.74 1.25
22.10 21.31 20.74 21.24
± ± ± ±
7.10 3.62 5.56 2.81
Table III. Endurance Time on both legs before and after training Right leg (s) Group LW UW DW MW
Before 56 54 67 65
± ± ± ±
24 28 31 19
Left leg (s)
After 66 60 63 65
± ± ± ±
23 25 32 9
Before 56 53 71 61
± ± ± ±
28 31 34 23
After 61 58 70 69
± ± ± ±
32 21 49 20
European Journal of Sport Science Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tejs20
Downhill walking to improve lower limb strength in healthy young adults a
Angelo Rodio & Luigi Fattorini
b
a
Department of Human Sciences, Society and Health, University of Cassino e Southern Lazio, Cassino (FR), Italy b
Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Rome, Italy Published online: 23 Apr 2014.
Click for updates To cite this article: Angelo Rodio & Luigi Fattorini (2014) Downhill walking to improve lower limb strength in healthy young adults, European Journal of Sport Science, 14:8, 806-812, DOI: 10.1080/17461391.2014.908958 To link to this article: http://dx.doi.org/10.1080/17461391.2014.908958
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
European Journal of Sport Science, 2014 Vol. 14, No. 8, 806–812, http://dx.doi.org/10.1080/17461391.2014.908958
ORIGINAL ARTICLE
Downhill walking to improve lower limb strength in healthy young adults
ANGELO RODIO1 & LUIGI FATTORINI2 1
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
2
Department of Human Sciences, Society and Health, University of Cassino e Southern Lazio, Cassino (FR), Italy; Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Rome, Italy
Abstract Walking is the most natural physical activity to maintain and improve fitness and health. Walking downhill is usefully adopted to plan training programmes to improve the strength, particularly in older adults. The present research was aimed to evaluate the influence of downhill walking on leg strength in young adult. A total of 32 females (age 26 ± 4 years; height 1.64 ± 0.05 m; body mass 57.6 ± 5.6 kg) were divided into four groups and they carried out an exercise intervention consisting of three sessions per week for 6 weeks, each lasting 30 minutes. Groups were defined at several workloads characterised by treadmill inclination (%) and walking speed (m·s−1): Level Walking at treadmill inclination 0% and walking speed 1.0; Uphill Walking at +20%, 0.75; Downhill Walking (DW) at −20%, 1.36; and Mixed Walking at +20%, 0.75 and −20%, 1.36 each lasting 15 minutes. Maximum voluntary contraction (MVC) developed by the Quadriceps Femoris and Endurance Time at 60% MVC were evaluated before and after experimental period. At the end of each session, Borg’s scale and Visual Analogue Scale (VAS) were adopted in order to evaluate perception of rate exertion and pain. Statistical analysis showed significant only in MVC for DW in both right and left legs. Borg’s scale and VAS described light activity free of pain. Present findings showed how an eccentric exercise, short lasting and at a low workload, can be useful in inducing improvements in leg strength. Keywords: Sedentary, eccentric training, workload, slope, optimal speed
Introduction Physical inactivity is a specific condition largely diffuse within populations of industrial countries. Sedentary lifestyles, as a consequence of physical inactivity, are to be found in every age from childhood to the elderly in both genders. Sedentariness increases all causes of mortality, the risk of cardiovascular diseases and obesity, as well as the risk of colon cancer, high blood pressure, depression and anxiety. According to Bonow, Smaha, Smith, Mensah, and Lenfant (2002) on the basis of the WHO report, 60–85% of people in the world—from both developed and developing countries—lead sedentary lifestyles, making it one of the most serious public health problems. Recently, Campbell et al. (2013) have shown in young adults lower levels of force values in comparison to the norm owing to sedentary habits. But, low strength values, just in the younger, over time could induce an aggravation
of physiological decay (Grimby & Saltin, 1986; Haskell et al., 2007; Lindle et al., 1997). It has been proved that eccentric muscle contraction is a valid form of physical exercise able to cause increases in maximal force by inducing hypertrophy of type II muscle cells (Fridèn, Seger, Sjostrom, & Ekblom, 1983; Fridèn, 1984; Roig et al., 2009). Eccentric contractions (ECCs) are muscular activations requiring force generation during lengthening, typically occurring when a muscle opposes a stronger force, which causes the muscle to lengthen as it contracts. Several daily activities bring into play an ECC such as going downstairs, walking or running downhill, lowering weights, the downward motion of squats and push-ups/pull-ups. Several training protocols have been proposed to increase absolute force using ECCs (Marcus, LaStayo, Dibble, Hill, & McClain, 2009) whereas, in the same context, the present paper explores the possibility of using walking downhill as a training
Correspondence: Luigi Fattorini, Department of Physiology and Pharmacology “V. Erspamer”, Sapienza University of Rome, Piazz.le Aldo Moro, 5, 00185 Rome, Italy. E-mail: [email protected] © 2014 European College of Sport Science
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
Downhill walking and lower limb strength tool. In fact, walking on negative slopes requires the nervous system to define contemporarily and in parallel two complex motor tasks: gait and balance. On negative slopes, the centre of mass is in front of the sagittal plane and, in steady stance, muscular activation must be present to counteract loss of stability in particular on leg and trunk muscles (among others quadriceps femori, adductor longus, adductor magnus, gluteus maximus, trapezius and latissimus). Moreover, walking is considered an effective physical activity for the maintenance and improvement of aerobic fitness (Haskell et al., 2007), for the prevention of cardiovascular and metabolic diseases, as reported by the American College Sports Medicine guidelines, and it may also be performed as a pleasant natural outdoor activity (American College of Sports Medicine [ACSM], 2005; Fattorini et al., 2012; Williams, 2008). Recently, walking downhill has been proposed as physical activity to improve functional mobility and force in older adults (Gault, Clements, & Willems, 2012; Gault, & Willems, 2013). The treadmill slope concept as used by Gault et al. (2012) and Gault and Willems (2013) was set at –10% because this is the point at which minimum total body energy cost occurs for downhill walking (Ardigò, Saibene, & Minetti, 2003). Gault et al.’s (2012) findings showed as maximal isokinetic force on lower limbs was not modified after exercise intervention, whilst mobility capacity increased, which could be a reflection of improved balance and coordination but not of strength changes. In a previous paper, the same authors argued that similar experimental conditions induced a muscular injury (Gault, Clements, & Willems, 2011) because the maximal leg force decreased 48 hours after with respect to baseline and it is a well-known fact that muscle cell trauma is a typical procedure which increases muscular force (LaStayo, Pierotti, Pifer, Hoppeler, & Lindstedt, 2000; Lindstedt, LaStayo, & Reich, 2001). Finally, in a more recent paper, which assessed isometric maximal contractions, Gault and Willems (2013) obtained an increase of about 5% in leg force in healthy older adults. The present research was designed to propose a physical intervention in young adults in order to counteract a decrease in force due to physical inactivity in this population. It is a well-known fact that generally, above 60 years of age, a physiological decline in musculoskeletal function, balance and mobility can be seen (Nolan, Nitz, Low Choy, & Illing, 2010). Hence, it is credible to argue that in young subjects the workload must be higher than in older ones to obtain comparable functional changes. For this reason, authors chose to increase the physical intervention intensity with respect to Gault
807
and Willems (2013) by implementing a steeper downhill treadmill inclination. The aim of the present study was to assess shortterm changes in muscle strength in a healthy young population using a 6-week long exercise intervention consisting of walking downhill on a treadmill set at a −20% gradient for three sessions per week. Materials and methods Subjects A total of 32 young adult female students were enrolled for the study (age 26 ± 4 years; height 1.64 ± 0.05 m; body mass 57.6 ± 5.6 kg; body mass index 21.4 ± 1.8 kg m−2). All individuals referred a moderate level of physical activity, confirming that they had not been involved in any kind of systematic training for at least 6 months prior to the present study. Also during the experimental period subjects were asked to avoid any other form of physical activity. Exclusion criteria included major neurological disorders, major musculoskeletal diseases or recent musculoskeletal injuries and cardiovascular disease. All subjects signed an informed consent after reading a description and scope of the experimental protocol. Institutional ethics committee approval was received for all study procedures, and the study conformed to the provisions of the Declaration of Helsinki. Exercise intervention protocol A week before the exercise intervention programme onset, all subjects visited the lab in order to familiarise with all experimental procedures. They were invited to walk on the treadmill under three different conditions per inclination and speed, each lasting about 5 minutes: 0% at 1.0 m·s−1; +20% at 0.75 m·s−1; and −20% at 1.36 m·s−1. Once the exercise intervention protocol began, all subjects underwent three sessions per week for 6 weeks, each session lasting 30 minutes. Within this context, subjects were randomly divided into four groups, each assigned to one of the following walking conditions on the treadmill (Runrace, Technogym, Italy) based on inclination and speed: Level Walking (LW) 0% at 1.0 m·s−1; Uphill Walking (UW) +20% at 0.75 m·s−1; Downhill Walking (DW) −20% at 1.36 m·s−1; and Mixed Walking (MW) at +20%, 0.75 m·s−1and at −20%, 1.36 m·s−1 each lasting 15 minutes. Negative Treadmill slopes were obtained by means of a customised phase inverter in order to generate the motor revolution in reverse cycle. Each speed was chosen in order to minimise the walking energy cost at aforementioned inclinations in accordance with Ardigò et al. (2003).
808
A. Rodio & L. Fattorini
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
Measurements For each subject, measurements of body composition, lower limb exerted force and Endurance Time (ET) were carried out a week before and after the experimental protocol. Body composition was determined by body fat mass evaluation using the nine-skinfold method and was reported as a percentage of total body mass (Jackson, Pollock, & Ward, 1980). Maximum voluntary contraction (MVC) developed by the Quadriceps Femoris was evaluated. Three maximal contraction attempts, each separated by a 5-minute rest, were performed and the maximal force measured was taken as the MVC value. Quadriceps Femoris ET at 60% MVC in isometric conditions was carried out on both legs, as the fatigue index. Banister (1979) has proven that there is only a small difference between exertion perception at 60% MVC and maximum perception of the effort of which the individual thinks he is capable. It is evident that 60% MVC is easier to maintain than MVC in especially in a no skilled population, therefore 60% MVC was chosen. During MVC and ET tests, the subject was seated in a customised chair; the vertical plan of the chair was adjustable in rotation and translation to set hip and knee angles at 110° and 90°, respectively, and capable of adapting to the individual’s anthropometric parameters. The subject’s hips and shoulders were restrained with straps and the arms folded to avoid the possibility of other muscles being involved in the movement. After a period of familiarisation with the experimental apparatus, the subject was encouraged to develop the force as fast as possible. The subject wore a boot on the side being examined with a special orthesis that locked the ankle joint at 90° and a ring was placed on the rear side connecting the piezoelectric force transducer (type 9311A, Kistler, Switzerland) to the chair. Force signal was amplified with a charge amplifier (type 5006, Kistler, Switzerland) and stored via an A/D converter (ATMIO, 12 bit, sample frequency 2048, National Instruments, USA) on a desktop computer. Force values were expressed as kilograms. ET test at 60% MVC in isometric conditions was carried out after at least 30 minutes from the last maximal contraction performed. This consisted in maintaining as much as possible the target force level showed on a screen. ET was computed offline as the time period where subject’s force was maintained stable on target around an error of 10%. This test was performed in the same MVC set-up. At the end of each training session, all subjects filled out two reports in order to describe rate of perceived exertion and pain following a 6–20 Borg’s
scale (Borg, 1998) and a 0–10 cm Visual Analogue Scale (VAS; Noble et al., 2005). Leg dominancy In the present study, three standard tests were used to establish leg dominancy; these were all performed before the comprehensive experimental protocol. The tests consisted of the following procedures: .
.
.
The subject had to step onto a platform (40 cm), where the leading leg spontaneously chosen by the subject was considered to be the dominant leg; In a standing up position with feet parallel, subjects were pushed forcefully from behind between the shoulder blades and the leg with which they attempted to regain their balance was considered the dominant leg; Lastly, subjects were asked with which leg they kicked a ball. Here again, the chosen leg was considered to be dominant.
In the present study, the dominant leg was defined as the leg that was dominant in at least two of the three tests. To check for consistency, the step test and the balance recovery test were repeated in between the dynamometer tests on both legs and again at the end of the first session. Statistical analysis Statistical analysis was undertaken using StatView for Windows ver. 5.0.1 (SAS, Cary, NC, USA). All data are expressed as means and relative standard deviations. A two-way repeated measures analysis of variance (ANOVA) was used to examine the change from all time points and between all conditions for all parameters. If this analysis evidenced significant differences, a paired Student’s t-test (Bonferroni corrected) to compare the mean values of the measured parameters before and after training protocol was used. Moreover, statistical power and sample size was performed. Significant statistical level was set at p < 0.05. Results Table I shows subjects’ anthropometric characteristic data and fat mass percentage. As can be seen, subjects were divided into four groups according to relative walking tasks where no differences among groups were recognised by statistical analysis. During the experimental phase, four subjects left the exercise programme, of which two in MW group (mixed), one in LW (flat) and one in DW (downhill) due to personal and not experimental reasons.
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Downhill walking and lower limb strength Table I. Subjects’ anthropometric characteristics on the four groups (data presented as mean and SD) Group
Age (years)
Downloaded by [University of Saskatchewan Library] at 06:49 30 January 2015
LW UW DW MW
26 27 24 24
± ± ± ±
Height (m)
6 4 3 4
1.62 1.62 1.64 1.69
± ± ± ±
Body mass (kg)
0.05 0.06 0.04 0.03
61.67 57.89 57.77 60.60
A prevalence of right-leg dominance was found for all four groups except in two subjects, belonging to MW and UW. In all groups, fat and body mass values before (Table I) and after the experimental programme were not statistically different (p > 0.05). Absolute force values were in a range between 190–390 N for right leg and 190–380 N for left leg; no statistical differences were recognised between legs and groups. Same measurements expressed as kilograms scaled by body mass, before and after exercise programme, are shown in Table II. ANOVA did not show differences between legs and groups at baseline, F(3, 28) = 2.461; p = 0.127, and after the intervention, F(3, 24) = 1.248; p = 0.314. In all groups, strength values were increased from baseline to post-intervention but resulted statistically different only in DW group for both legs (t(6) = 6.708; p < 0.001, and t(6) = 5.195; p < 0.001, in right and left legs, respectively). Also significant differences were obtained in MW, but the sample size in post-intervention, due to the drop out, did not guarantee the statistical power of the test so the Hypothesis 1 was rejected. ET values are shown in Table III. Here again, no statistical differences were to be seen between legs and groups. On the grounds of VAS tests carried out during the 18 sessions (total of 6 weeks), the perception of pain showed no change for LW (0%), MW and UW (20%). Whilst for DW (−20%) equivalent, VAS findings showed an increase in the perception of pain up to the third session where a peak value of 3 was to be seen, after which values already returned to Table II. Force values scaled by body mass before and after training Right leg (a.u.) Group LW UW DW MW
Before 0.44 0.51 0.47 0.41
*p < 0.05.
± ± ± ±
0.11 0.16 0.09 0.12
Left leg (a.u.)
After 0.51 0.58 0.57 0.49
± ± ± ±
0.14 0.13 0.09* 0.11
Before 0.45 0.51 0.45 0.40
± ± ± ±
0.11 0.13 0.06 0.06
After 0.51 0.56 0.57 0.51
± ± ± ±
0.12 0.18 0.11* 0.11
± ± ± ±
Body mass index (kg m−2)
7.34 6.86 5.28 5.13
23.55 22.06 21.52 21.14
± ± ± ±
Fat mass (%)
6.90 2.61 1.74 1.25
22.10 21.31 20.74 21.24
± ± ± ±
7.10 3.62 5.56 2.81
Table III. Endurance Time on both legs before and after training Right leg (s) Group LW UW DW MW
Before 56 54 67 65
± ± ± ±
24 28 31 19
Left leg (s)
After 66 60 63 65
± ± ± ±
23 25 32 9
Before 56 53 71 61
± ± ± ±
28 31 34 23
After 61 58 70 69
± ± ± ±
32 21 49 20
