with a curved force-velocity relationship similar to that in frog's muscle. The the angle of flexion, and this function is different for each of the five muscles. The advantage of this paired arrangement of gauges is that temperature effects are. This first paragraph will focus on muscle temperature and muscle function. .. Temperature and force-velocity relationship of human muscle. J Appl Physiol . Force-velocity data at different temperatures (range, °C) from intact fibre bundles are muscle function in the body. and the P-V relation in mammalian (rat) fast and slow muscle fibres (Ranatunga, , ).
All these data come from power output recorded during cycling test, but the explanations for these different sensibilities to a warm environment is still unclear. An interesting explanation could be the recently developed hypothesis of a threshold in the beneficial effect of increasing body temperature Racinais et al b, a, Basically, the endogenous diurnal increase in body temperature i. In line with this hypothesis, it is generally observed an increase in muscular power during the day in parallel to the circadian increase in body temperature Reilly and Down, Bernard et alMelhimRacinais et al b and a.
This study raised intriguing questions about the cause of this stability. Two suggestions seemed reasonable: Some recent studies comparing diurnal variation i. Interestingly, a warm environment allows to improve muscle power Racinais et al b and contractility a in the morning only, when body temperature were at their lowest. This suggests that these two passive warm-up effects have no additional effect on the improvement in muscle power. From Muscle contraction to repeated or prolonged exercise Effect of exercise duration.
This introduction points the possibility of an improvement in muscle power production after heating the muscle by a hot bath e. However, an elevated body temperature seems to be a limiting factor for performance of prolonged, intermittent, high-intensity running in warm environment Morris et al Furthermore, it exist also a lot of evidence pointing hyperthermia has a key limiting factor for long duration exercise in warm environment see the other chapters of this website.
If an increase in muscle temperature may improve power production during short duration exercise but an increase in body core temperature limit prolonged exercise, the question is to known how and when the shift from improvement to impairment in physical ability occurs. The model of repeated exercise could provide some answer about this shift.
Indeed, the repetition of maximal exercise allows to investigate the evolution of the performance with considering heat produced during the first exercise s leading an increase in body core temperature in the following exercise sespecially in hot or warm and humid environment.
However, the relatively long recovery period allowed i. Interestingly, equivalent data were also observed with shorter recovery period i. These studies observed either an improvement in power output in warm environment Falk et al or not Backx et al but both of them failed to observed significant effect of the environmental condition on the performance decrement with the exercise repetition. Taking together, these data suggest that a warm environment have no deleterious effect on the repetition of short-duration exercise.
Two hypotheses could be advanced to explain this observation. For the fastest stretch used, the contributions of cross-bridge and non-cross-bridge mechanisms were equal. For the slowest stretch, lasting 10 s and over the same distance, the force response was attributed almost entirely to non-cross-bridge mechanisms.
The transient component of the stretch response increased as a result of fatigue, relative to the isometric force, while the force during shortening decreased. The results are consistent with a decrease in cross-bridge turnover in fatigued muscle.
Temperature and force-velocity relationship of human muscles.
It is well documented that when activated skeletal muscle is stretched the force sustained by the muscle increases above maximal isometric values and that the additional force increases with increasing velocities of stretch Katz, ; Edman et al. Consequently a clear dependency of eccentric force on stretch velocity has not been demonstrated during voluntary efforts. The differences between studies on human muscle and isolated preparations may be due to inhibition of neural drive during voluntary contractions Westing et al.
For example, eccentric-to-isometric force ratios of about 1.
The response of active muscle to stretch is complex even in isolated and single fibre preparations and the nature of the different phases of the response is not clearly understood Noble, Adding additional external compliance, as with muscle working in vivo, further complicates the interpretation of the data.
It is important, however, to address the question of stretch of muscle-tendon complexes working in vivo since, ultimately, this is how the skeletal muscles are used. The first point addressed in the present study is the contribution of the cross-bridge components of the stretch response in relation to other elements, possibly to series and parallel elements. There are ample indications that there are different components to the stretch response.
Not only is force enhanced during the stretch but also the isometric force remains elevated for some time after the movement has finished e. The analysis used by Noble was suitable for single fibre preparations; it remains to be seen whether it is also applicable to large muscle-tendon complexes working in vivo.
Muscle Contraction and Temperature
The second question addressed here concerns the effect of fatigue on the response of the whole muscle-tendon complex to stretch. High intensity, metabolically demanding exercise leads to a considerable loss of muscle power, as has been shown in fatigued animal De Haan et al.
Whilst many fundamental mechanisms are common to all skeletal muscles, the balance between potential rate limiting steps during fatigue may vary between amphibian and mammalian muscles. Examples of this are the contribution of calcium re-uptake during relaxation Allen et al. The objective of the work described here was firstly to characterise the stretch response of the human adductor pollicis stimulated to contract in vivo and, secondly, to determine to what extent the different components of the response are affected by fatigue.
Temperature and force-velocity relationship of human muscles.
METHODS Subjects The study was approved by the local ethical committee and eight healthy female subjects aged years took part after giving their written informed consent. Female subjects were selected because in male subjects, who have, in general, larger and stronger hands, the motor system was not powerful enough to stretch at high velocities the adductor pollicis muscle. The subjects were all right handed and did not undertake any regular exercise that particularly involved the hand muscles.