Relationships between muscle fatigue characteristics and markers of endurance performance

The aim of this study was to examine the relationship of a range
of in-vivo whole muscle characteristics to determinants of endurance
performance. Eleven healthy males completed a cycle
ergometer step test to exhaustion for the determination of the
lactate threshold, gross mechanical efficiency, peak power and
VO2max. On two separate occasions, contractile and fatigue
characteristics of the quadriceps femoris were collected using a
specially designed isometric strength-testing chair. Muscle
fatigue was then assessed by stimulating the muscle for 3 minutes.
Force, rate of force development and rates of relaxation
were calculated at the beginning and end of the 3 minute protocol
and examined for reliability and in relation to lactate threshold,
VO2max, gross mechanical efficiency and peak power.
Muscle characteristics, rate of force development and relaxation
rate were demonstrated to be reliable measures. Force drop off
over the 3 minutes (fatigue index) was related to lactate threshold
(r = -0.72 p < 0.01) but not to VO2max. The rate of force
development related to the peak power at the end of the cycle
ergometer test (r = -0.75 p < 0.01). Rates of relaxation did not
relate to any of the performance markers. We found in-vivo
whole muscle characteristics, such as the fatigue index and rate
of force development, relate to specific markers of peripheral,
but not to central, fitness components. Our investigation suggests
that muscle characteristics assessed in this way is reliable
and could be feasibly utilised to further our understanding of the
peripheral factors underpinning performance.