Fatigue during sustained maximal voluntary contraction of different muscles in humans: dependence on fibre type and body posture

Abstract

Nine healthy men, aged between 25 and 35 years, performed sustained maximal voluntary contractions (MVC) of foot plantar, foot dorsal, and finger flexor muscles. Contractions lasted 10 min and were followed by short test contractions at 30% MVC during recovery. Two positions of the working extremity high or low were established by different body postures (supine or sitting). Under these conditions, studies of force, integrated electromyogram (iEMG), blood pressure, and heart rate showed firstly that force decreased throughout the first few minutes of maximal contraction but reached a near steady-state value after 5 to 6 min. Secondly, force decay and steady-state level depended on muscle group and body position. When sitting (low leg), muscles with a high incidence of slow twitch fibres (plantar flexors) showed a slower force decay and a higher relative steady-state force than fast dorsal flexor muscles. When supine (high leg), plantar and dorsal flexor muscles reached about the same low level of relative steady-state force. Changes in iEMG, blood pressure, and heart rate did not differ in the two positions. Thirdly, during recovery, plantar flexor muscles showed higher iEMG values as well as higher values of blood pressure and heart rate when supine than when sitting. Recovery of dorsal flexor muscles was little affected by body posture. Fourthly, force development and recovery of predominantly fast finger flexor muscles were almost independent of arm position. It was concluded that muscle fibre composition was the main factor in determining endurance capacity. However, endurance was influenced by changes in the hydrostatic blood pressure component.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of grip types and intensities on force-decreasing curves and physiological responses during sustained muscle contractions

“…The force output during sustained muscle contractions with moderate or high intensity decreases with time lapses, and reaches an almost steady state [6][7][8][9]15]. The present force decreasing property agreed with those in the previous reports except for an IRG test with 50% MVC, in which almost all subjects could maintain greater than target force with little decrease.…”

“…In the case of sustained isometric contractions above 50% MVC, the force output decreases markedly in the initial phase and reaches an almost steady state at 15-20% MVC within 150-180 s [4,[6][7][8][9] With intermittent repeated muscle contractions, the force output is largely influenced by an exertion interval as well as sustained time [10] because of repeated muscle contraction and relaxation. Summarizing previous findings on the exertion interval, a repeated contraction with a 2 s interval using high intensity reaches an almost steady state within about 180 s, but not until at 6 min with over a 2 s interval [3,4,10].…”

Energy metabolism in intensively exercising calf muscle under a simulated orthostasis

“…After 3 min of isometric contraction under LBNP, m. tibialis anterior showed a higher loss in force, a larger PCr consumption and a larger decrease in pH. The observations on m. tibialis anterior seem to be in contrast to the enhancements in fatigue resistance observed in calf and upper leg muscles at real or simulated orthostasis [4,12]. However, m. tibialis anterior may generally behave different to the load bearing upper leg muscles and the calf muscle.…”

“…However, the alterations in fatigue resistance by posture do not only depend on variations in blood flow. For arm and leg muscles working in a sustained isometric mode, it was shown that differences in fibre type compositions of muscles also contribute to different sensitivities to alterations in posture concerning the development of fatigue [4].…”

A mathematical model-based approach to optimize loading schemes of isometric resistance training sessions

“…To the best of our knowledge, no prediction of endurance time or work capacity exists for MVIC efforts. Caffier et al [16], for example, examined MVIC efforts of several muscle groups lasting 10 min and reported no task failure among the subjects. Thus, it remains to be validated experimentally if the solutions of Session A, E, and G, which contain sustained MVIC efforts of long durations, can be realized in practice.…”