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Physiological Responses at the Fatigue Threshold T J. Housh, G. 0. Johnson, S. L. McDowell, D. J. Housh, M Pepper Center for Youth Fitness and Sports Research, University of Nebraska-Lincoln
T. J. Housh, G. 0. Johnson, S. L. McDowell, D. J. Housh, and M Pepper, Physiological Responses at the Fatigue Threshold. mt J Sports Med, Vol 12, No 3, pp305 — 308, 1991.
Accepted: August 14, 1990
The purpose of this investigation was to determine the oxygen consumption, heart rate and plasma lactate responses at the fatigue threshold (FT) and estimate the length of time the FT could be maintained. Ten adult
males (ii age SD 21.1 1.3 yrs) volunteered to perform a maximal treadmill test and FT test. During the maximal test, V02, heart rate and plasma lactate measurements
were taken. The results of the investigation indicated that
the FT (14.0±1.2 kmhr 197±8 bpm; 47.5±5.7 ml/kgmin
5.4± 1.3 mM) was very close to a maximal
effort (VO2max 14.4±1.2 kmhr, 203±10 bpm; 49.5±6.1 ml/kgmin 7.4±2.1 mM) and could be maintained for only 0.16 to 0.28 hrs. These findings do not support the validity of the FT as a measure of the maximal running velocity that can be continued for an extended period of time without exhaustion. Key words
Fatigue threshold, VO2max, physiological responses
between velocity and the inverse of time to exhaustion (1 /TL). Theoretically, the FT is the asymptote of the hyperbolic rela-
tionship between velocity and TL. Although there are many potential uses for the parameters derived from the FT test, there is very little information concerning their validity. Therefore, the purpose of this study was to examine the validity of the FT by determining the oxygen consumption, heart rate and plasma lactate responses at the FT and estimate the length of time the FT could be maintained. Materials and Methods
Ten adult males (w age SD 21.1
1.3
yrs; height= 179.7±4.2 cm; weigth=76.9±8.2 kg) volunteered as subjects for this investigation and gave informed consent prior to testing. The subjects utilized by Hughson et al. (4)
were highly motivated university cross-country runners
ml/kgmin 1) who were capable of maintaining running velocities of 19.2 to 22.4 kmhr for 2 to 12 minutes. The physically active subjects in the present study (VO2max 41.9—60.3 ml/kg'min') were not as aerobically trained as those of Hughson et al. (4) but were regularly in(VO2max = 65—73
volved in such activities as bicycling, jogging or weight training. At the time of testing, the subjects were running from 0 to 15 miles per week.
On the first laboratory visit, the subjects performed a continuous incremental treadmill test for the determination of maximal oxygen consumption rate (VO2max) (Table 1). The treadmill test began at 6.4 knvhr and in1
creased 1.6 kmhr every three minutes up to 14.5 kmhr The intensity was then increased by raising the treadmill grade 2 % every three minutes (with the speed remaining constant at
Introduction
Hughson et al. (4) developed a treadmill test which, theoretically, provides estimates of the maximal running velocity that can be maintained for an extended period of time without exhaustion (called the fatigue threshold =FT)
14.5 knvhr5 until voluntary exhaustion. Throughout the test, the subjects breathed through a Hans Rudolph valve with the gas volume (VE) and concentrations (FEO2 and FECO2)
analyzed using a calibrated MMC Horizon Metabolic
Measurement Cart (Sensor Medics Corporation, Anaheim, CA). The VO2max was defined as the highest measured V02 and indirect assessments of anaerobic capabilities. The FT value test given a plateau of V02 with increased work intensity involves a series of high speed treadmill runs to exhaustion at and/or respiratory quotient > 1.15 (7,12). The subjects' heart several different velocities during which the time to exhaus- rate values were monitored throughout the test using a IJNIQ tion or time limit (TL) is recorded. Essentially, this technique is CIC Heartwatch system (6). In addition, blood samples were a treadmill analog of previous tests which have utilized cycle drawn by a trained phiebotomist from an indwelling catheter ergometry or synergic muscle groups (2,3, 8. 10, 11).
lnt.JSportsMed. 12(1991)305308 GeorgThieme Verlag Stuttgart New York
placed in the antecubital vein during the final thirty seconds of each treadmill stage. The samples were analyzed for plasma lactate levels using a YSI Model 23L lactate analyzer (Yellow Springs Instrument Company, Yellow Springs, Ohio).
Downloaded by: NYU. Copyrighted material.
Abstract
The FT and anaerobic component are defined as the y-intercept and slope, respectively, of the relationship
306 mt. J. Sports Med. 12 (1991) Table 1
T. J. Housh, G. 0. Johnson, S. L. McDowell, D. .1. Housh, M. Pepper
Physiological responses of the subjects SD
1. 2.
VOmax (ml/kgmin) VO2max (kmhr)
3. 4. 5. 6.
Maximal Heart Rate (bpm) Maximal Plasma Lactate (mM)
7.
8. 9. 10. 11. 12. 13. 14.
203.0
6.1
1.2 10.0
7.4 4.0
2.1
Plasma
1.2
4.0
Fatigue Threshold (bpm) Fatigue Threshold (% of Max bpm)
97.0 197.0 97.0
Lactate (mM)
Fatigue Threshold (ml/kgmin
47.5
5.7
(% of Max ml/kgmin)
96.0
4.0
Fatigue Threshold (mM Lactate) Fatigue Threshold (% of Max mM Lactate) Predicted Velocity for a TL
5.4 75.0
16.0
of 0.5 hr (kmhr*
12.1
1.6
10.8 0.21
0.03
Fatigue Threshold (kmhr Fatigue Threshold (% of Max kmhr
at FT
8.0 2.0
Fatigue Threshold 1.3 FT
v02 (ml/kg.min1)
Predicted Velocity for a TL
of 1.0 hr (kmhr' 15.
49.5 14.4
Predicted TL at the FT (hrs) *
1.7
Fig. 1 An illustration of the method used to determine the plasma lactate value corresponding to the fatigue threshold (FT).
* Predicted values based on power curve analysis between velocity and IL using the mean values for the total sample (see Fig. 2).
sponding to the FT and the percents of maximal values the FT The FT was determined using the procedures described by Hughson et a!. (4). The subjects completed four randomly ordered treadmill runs to exhaustion on seqarate
days at velocities ranging from 14.5 to 19.3 kmhr . The velocities were selected based on the subject's fitness level
such that each run would last for approximately 2 to 12 minutes (4). Prior to each run, the subject practiced getting on and off the treadmill at the velocity associated with that workbout to familiarize himself with the running speed. Timing for each treadmill run began when the subject released the handrails (usually 2—3 seconds after getting on the treadmill) and was terminated when the subject grasped the handrails to si-
A paired t-test indicated that there was no sig-
nificant difference (t== 1.99, df=9; p>O.O5) between the
FT ( SEM 14.0 0.4 kmhr') and the running velocity corresponding to VO2max (14.4 0.4 kmhr 5. There were,
however, significant (t = 2.78; p
Physiological Responses at the Fatigue Threshold T J. Housh, G. 0. Johnson, S. L. McDowell, D. J. Housh, M Pepper Center for Youth Fitness and Sports Research, University of Nebraska-Lincoln
T. J. Housh, G. 0. Johnson, S. L. McDowell, D. J. Housh, and M Pepper, Physiological Responses at the Fatigue Threshold. mt J Sports Med, Vol 12, No 3, pp305 — 308, 1991.
Accepted: August 14, 1990
The purpose of this investigation was to determine the oxygen consumption, heart rate and plasma lactate responses at the fatigue threshold (FT) and estimate the length of time the FT could be maintained. Ten adult
males (ii age SD 21.1 1.3 yrs) volunteered to perform a maximal treadmill test and FT test. During the maximal test, V02, heart rate and plasma lactate measurements
were taken. The results of the investigation indicated that
the FT (14.0±1.2 kmhr 197±8 bpm; 47.5±5.7 ml/kgmin
5.4± 1.3 mM) was very close to a maximal
effort (VO2max 14.4±1.2 kmhr, 203±10 bpm; 49.5±6.1 ml/kgmin 7.4±2.1 mM) and could be maintained for only 0.16 to 0.28 hrs. These findings do not support the validity of the FT as a measure of the maximal running velocity that can be continued for an extended period of time without exhaustion. Key words
Fatigue threshold, VO2max, physiological responses
between velocity and the inverse of time to exhaustion (1 /TL). Theoretically, the FT is the asymptote of the hyperbolic rela-
tionship between velocity and TL. Although there are many potential uses for the parameters derived from the FT test, there is very little information concerning their validity. Therefore, the purpose of this study was to examine the validity of the FT by determining the oxygen consumption, heart rate and plasma lactate responses at the FT and estimate the length of time the FT could be maintained. Materials and Methods
Ten adult males (w age SD 21.1
1.3
yrs; height= 179.7±4.2 cm; weigth=76.9±8.2 kg) volunteered as subjects for this investigation and gave informed consent prior to testing. The subjects utilized by Hughson et al. (4)
were highly motivated university cross-country runners
ml/kgmin 1) who were capable of maintaining running velocities of 19.2 to 22.4 kmhr for 2 to 12 minutes. The physically active subjects in the present study (VO2max 41.9—60.3 ml/kg'min') were not as aerobically trained as those of Hughson et al. (4) but were regularly in(VO2max = 65—73
volved in such activities as bicycling, jogging or weight training. At the time of testing, the subjects were running from 0 to 15 miles per week.
On the first laboratory visit, the subjects performed a continuous incremental treadmill test for the determination of maximal oxygen consumption rate (VO2max) (Table 1). The treadmill test began at 6.4 knvhr and in1
creased 1.6 kmhr every three minutes up to 14.5 kmhr The intensity was then increased by raising the treadmill grade 2 % every three minutes (with the speed remaining constant at
Introduction
Hughson et al. (4) developed a treadmill test which, theoretically, provides estimates of the maximal running velocity that can be maintained for an extended period of time without exhaustion (called the fatigue threshold =FT)
14.5 knvhr5 until voluntary exhaustion. Throughout the test, the subjects breathed through a Hans Rudolph valve with the gas volume (VE) and concentrations (FEO2 and FECO2)
analyzed using a calibrated MMC Horizon Metabolic
Measurement Cart (Sensor Medics Corporation, Anaheim, CA). The VO2max was defined as the highest measured V02 and indirect assessments of anaerobic capabilities. The FT value test given a plateau of V02 with increased work intensity involves a series of high speed treadmill runs to exhaustion at and/or respiratory quotient > 1.15 (7,12). The subjects' heart several different velocities during which the time to exhaus- rate values were monitored throughout the test using a IJNIQ tion or time limit (TL) is recorded. Essentially, this technique is CIC Heartwatch system (6). In addition, blood samples were a treadmill analog of previous tests which have utilized cycle drawn by a trained phiebotomist from an indwelling catheter ergometry or synergic muscle groups (2,3, 8. 10, 11).
lnt.JSportsMed. 12(1991)305308 GeorgThieme Verlag Stuttgart New York
placed in the antecubital vein during the final thirty seconds of each treadmill stage. The samples were analyzed for plasma lactate levels using a YSI Model 23L lactate analyzer (Yellow Springs Instrument Company, Yellow Springs, Ohio).
Downloaded by: NYU. Copyrighted material.
Abstract
The FT and anaerobic component are defined as the y-intercept and slope, respectively, of the relationship
306 mt. J. Sports Med. 12 (1991) Table 1
T. J. Housh, G. 0. Johnson, S. L. McDowell, D. .1. Housh, M. Pepper
Physiological responses of the subjects SD
1. 2.
VOmax (ml/kgmin) VO2max (kmhr)
3. 4. 5. 6.
Maximal Heart Rate (bpm) Maximal Plasma Lactate (mM)
7.
8. 9. 10. 11. 12. 13. 14.
203.0
6.1
1.2 10.0
7.4 4.0
2.1
Plasma
1.2
4.0
Fatigue Threshold (bpm) Fatigue Threshold (% of Max bpm)
97.0 197.0 97.0
Lactate (mM)
Fatigue Threshold (ml/kgmin
47.5
5.7
(% of Max ml/kgmin)
96.0
4.0
Fatigue Threshold (mM Lactate) Fatigue Threshold (% of Max mM Lactate) Predicted Velocity for a TL
5.4 75.0
16.0
of 0.5 hr (kmhr*
12.1
1.6
10.8 0.21
0.03
Fatigue Threshold (kmhr Fatigue Threshold (% of Max kmhr
at FT
8.0 2.0
Fatigue Threshold 1.3 FT
v02 (ml/kg.min1)
Predicted Velocity for a TL
of 1.0 hr (kmhr' 15.
49.5 14.4
Predicted TL at the FT (hrs) *
1.7
Fig. 1 An illustration of the method used to determine the plasma lactate value corresponding to the fatigue threshold (FT).
* Predicted values based on power curve analysis between velocity and IL using the mean values for the total sample (see Fig. 2).
sponding to the FT and the percents of maximal values the FT The FT was determined using the procedures described by Hughson et a!. (4). The subjects completed four randomly ordered treadmill runs to exhaustion on seqarate
days at velocities ranging from 14.5 to 19.3 kmhr . The velocities were selected based on the subject's fitness level
such that each run would last for approximately 2 to 12 minutes (4). Prior to each run, the subject practiced getting on and off the treadmill at the velocity associated with that workbout to familiarize himself with the running speed. Timing for each treadmill run began when the subject released the handrails (usually 2—3 seconds after getting on the treadmill) and was terminated when the subject grasped the handrails to si-
A paired t-test indicated that there was no sig-
nificant difference (t== 1.99, df=9; p>O.O5) between the
FT ( SEM 14.0 0.4 kmhr') and the running velocity corresponding to VO2max (14.4 0.4 kmhr 5. There were,
however, significant (t = 2.78; p
