Reproducible Voluntary Muscle Performance During Constant Work Rate Dynamic Leg Exercise

During constant intensity treadmill or cycle exercise, progressive muscle fatigue is not readily quantified and endurance time is poorly reproducible. However, integration of dynamic knee extension (DKE) exercise with serial measurement of maximal voluntary contraction (MVC) force of knee extensor muscles permits close tracking of leg fatigue. We studied reproducibility of four performance indices: MVC force of rested muscle (MVC_rest) rate of MVC force fall, time to exhaustion, and percentage of MVC_rest (%MVC_rest) at exhaustion in 11 healthy women (22 ± 1 yrs) during identical constant work rate 1-leg DKE (1 Hz) on 2 separate days at sea level (30 m). Means ± SD for the two test days, and the correlations (r), standard estimate errors and coefficients of variation (CV%) between days were, respectively: a) MVC_rest (N), 524 ± 99 vs 517 ± 111, 0.91, 43.0, 4.9 %; b) MVC force fall (N × min^-1), - 10.77 ± 9.3 vs - 11.79 ± 12.1, 0.94, 3.6, 26.5 %; c) Time to exhaustion (min), 22.6 ± 12 vs 23.9 ± 14, 0.98, 2.7, 7.5 %; and d) %MVC_rest at exhaustion, 65 ± 13 vs 62 ± 14, 0.85, 7.8, 5.6 %. There were no statistically significant mean differences between the two test days for any of the performance measures. To demonstrate the potential benefits of evaluating multiple effects of an experimental intervention, nine of the women were again tested within 24 hr of arriving at 4300 m altitude using the identical force, velocity, power output, and energy requirement during constant work rate dynamic leg exercise. Low variability of each performance index enhanced the ability to describe the effects of acute altitude exposure on voluntary muscle function.

Key words:

Exercise - exhaustion - MVC - force - muscle fatigue - muscle function - leg extension

References

• 1 Bigland-Ritchie B, Woods J J. Integrated electromyogram and oxygen uptake during positive and negative work.  J Physiol (Lond). 1976;  260 267-277
• 2 Crenshaw A G, Karlsson S, Styf J, Backlund T, Friden J. Knee extension torque and intramuscular pressure of the vastus lateralis muscle during eccentric and concentric activities.  Eur J Appl Physiol. 1995;  70 13-19
• 3 Edwards R HT. Human muscle function and fatigue. In: Porter R, Whelan J (eds) Human Muscle Fatigue: Physiological Mechanisms. London; Pitman Medical 1981: 1-18
• 4 Fulco C S, Lewis S F, Frykman P, Boushel R, Smith S, Cymerman A, Pandolf K B. Quantitation of progressive muscle fatigue during dynamic leg exercise in humans.   J Appl Physiol. 1995;  79 2154-2162
• 5 Fulco C S, Lewis S F, Frykman P, Boushel R, Smith S, Cymerman A, Pandolf K B. Muscle fatigue and exhaustion during dynamic leg exercise in normobaria and hypobaria.   J Appl Physiol. 1996;  81 1891-1900
• 6 Jeukendrup A, Saris W HM, Brouns F, Kester A DM. A new validated endurance performance test.  Med Sci Sports Exerc. 1996;  28 266-270
• 7 Kroll W. Reliability variations of strength in test-retest situations.  Res Quart. 1963;  34 50-55
• 8 Lewis S F, Fulco C S. A new approach of studying muscle fatigue and factors affecting performance during dynamic exercise in humans. In: Holloszy JO (ed) Exercise and Sport Sciences Reviews. Baltimore, Maryland; Williams and Wilkins 1998: 91-116
• 9 Mannion A F, Jakeman P M, Willan P LT. Effects of isokinetic training of the knee extensors on isometric strength and peak power output during cycling.  Eur J Appl Physiol. 1992;  65 370-375
• 10 Tesch P A, Dudley G A, Duovoisin M R, Hather B M, Harris R T. Force and EMG signal patterns during repeated bouts of concentric and eccentric muscle actions.  Acta Physiol Scand. 1990;  138 263-271
• 11 Tornvall G. Assessment of physical capabilities (with special reference to the evaluation of maximal voluntary isometric muscle strength and maximal working capacity).  Acta Physiol Scand. 1963;  58 1-101
• 12 Zar J H. Biostatistical Analysis. Englewood Cliffs, NJ; Prentice-Hall 1984