Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia

TY - JOUR

T1 - Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia

AU - Fulco, C S

AU - Lewis, S F

AU - Frykman, Peter

AU - Boushel, Robert Christopher

AU - Smith, Susanne

AU - Harman, E A

AU - Cymerman, A

AU - Pandolf, K B

PY - 1996/11/1

Y1 - 1996/11/1

N2 - Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 +/- 3 W, 79 +/- 2 and 87 +/- 2% of 1-leg knee extension O2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90-150 degrees at a rate of 1 Hz. MVC (90 degrees knee angle) was performed before dynamic exercise and during 0.05) that were higher (P <0.01) than peak force of constant work rate knee extension (98 +/- 10 N, 18 +/- 3% of MVC). Time to exhaustion was 56% shorter for hypobaria than for normoxia (19 +/- 5 vs. 43 +/- 7 min, respectively; P <0.01), and rate of right leg MVC fall was nearly twofold greater for hypobaria than for normoxia (mean slope = -22.3 vs. -11.9 N/min, respectively; P <0.05). With increasing duration of dynamic exercise for normoxia and hypobaria, integrated electromyographic activity during MVC fell progressively with MVC force, implying attenuated maximal muscle excitation. Exhaustion, per se, was postulated to related more closely to impaired shortening velocity than to failure of force-generating capacity.

AB - Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 +/- 3 W, 79 +/- 2 and 87 +/- 2% of 1-leg knee extension O2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90-150 degrees at a rate of 1 Hz. MVC (90 degrees knee angle) was performed before dynamic exercise and during 0.05) that were higher (P <0.01) than peak force of constant work rate knee extension (98 +/- 10 N, 18 +/- 3% of MVC). Time to exhaustion was 56% shorter for hypobaria than for normoxia (19 +/- 5 vs. 43 +/- 7 min, respectively; P <0.01), and rate of right leg MVC fall was nearly twofold greater for hypobaria than for normoxia (mean slope = -22.3 vs. -11.9 N/min, respectively; P <0.05). With increasing duration of dynamic exercise for normoxia and hypobaria, integrated electromyographic activity during MVC fell progressively with MVC force, implying attenuated maximal muscle excitation. Exhaustion, per se, was postulated to related more closely to impaired shortening velocity than to failure of force-generating capacity.

KW - Adult

KW - Anoxia

KW - Atmospheric Pressure

KW - Electromyography

KW - Energy Metabolism

KW - Exercise

KW - Humans

KW - Leg

KW - Male

KW - Muscle Contraction

KW - Muscle Fatigue

KW - Oxygen

KW - Oxygen Consumption

KW - Physical Endurance

M3 - Journal article

C2 - 8941506

SN - 8750-7587

VL - 81

SP - 1891

EP - 1900

JO - Journal of Applied Physiology

JF - Journal of Applied Physiology

IS - 5

ER -