Force-velocity relationship of human muscle

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The research idea for this study came from Professor Anthony J Sargeant of Amsterdam and Professor David Jones (Birmingham University). It was the culmination of many years of Tony Sargeant encouraging members of his research group in Amsterdam to adapt a technique for studying rat muscle force velocity to small human hand muscles. The data was finally collected by Jo de Ruiter a post-doc in the Amsterdam research group.

The measurement of force/velocity relationships of fresh and fatigued human adductor pollicis muscle.

CJ De Ruiter, David A Jones, Anthony J Sargeant, Arnold de Haan.

European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1999 Sep;80(4):386-93
The purpose of the study was to obtain force/velocity relationships for electrically stimulated (80 Hz) human adductor pollicis muscle (n = 6) and to quantify the effects of fatigue. There are two major problems of studying human muscle in situ; the first is the contribution of the series elastic component, and the second is a loss of force consequent upon the extent of loaded shortening. These problems were tackled in two ways. Records obtained from isokinetic releases from maximal isometric tetani showed a late linear phase of force decline, and this was extrapolated back to the time of release to obtain measures of instantaneous force. This method gave usable data up to velocities of shortening equivalent to approximately one-third of maximal velocity. An alternative procedure (short activation, SA) allowed the muscle to begin shortening when isometric force reached a value that could be sustained during shortening (essentially an isotonic protocol). At low velocities both protocols gave very similar data (r2 = 0.96), but for high velocities only the SA procedure could be used. Results obtained using the SA protocol in fresh muscle were compared to those for muscle that had been fatigued by 25 s of ischaemic isometric contractions, induced by electrical stimulation at the ulnar nerve. Fatigue resulted in a decrease of isometric force [to 69 (3)%], an increase in half-relaxation time [to 431 (10)%], and decreases in maximal shortening velocity [to 77 (8)%] and power [to 42 (5)%].
These are the first data for human skeletal muscle to show convincingly that during acute fatigue, power is reduced as a consequence of both the loss of force and slowing of the contractile speed
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Oxygen cost of human exercise

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In this research published in Journal of Physiology Anthony Sargeant and his team describe how the recruitment of different types of muscle fibres with increasing exercise intensity changes the oxygen cost of exercise. Thus the relationship of oxygen uptake and mechanical power output is not constant. This is in contrast to the standard teaching of many physiology textbooks.

Non-linear relationship between O2 uptake and power output at high intensities of exercise in humans

Jerzy A. Zoladz, Arno C. H. J. Rademaker, Anthony J Sargeant

Journal of Physiology
J Physiol. 1995 Oct 1;488 ( Pt 1):211-7
1. A slow component to pulmonary oxygen uptake (VO2) is reported during prolonged high power exercise performed at constant power output at, or above, approximately 60% of the maximal oxygen uptake. The magnitude of the slow component is reported to be associated with the intensity of exercise and to be largely accounted for by an increased VO2 across the exercising legs.
2. On the assumption that the control mechanism responsible for the increased VO2 is intensity dependent we hypothesized that it should also be apparent in multi-stage incremental exercise tests with the result that the VO2-power output relationship would be curvilinear.
3. We further hypothesized that the change in the VO2-power output relationship could be related to the hierarchical recruitment of different muscle fibre types with a lower mechanical efficiency.
4. Six subjects each performed five incremental exercise tests, at pedalling rates of 40, 60, 80, 100 and 120 rev min-1, over which range we expected to vary the proportional contribution of different fibre types to the power output. Pulmonary VO2 was determined continuously and arterialized capillary blood was sampled and analysed for blood lactate concentration ([lactate]b).
5. Below the level at which a sustained increase in [lactate]b was observed pulmonary VO2 showed a linear relationship with power output; at high power outputs, however, there was an additional increase in VO2 above that expected from the extrapolation of that linear relationship, leading to a positive curvilinear VO2-power output relationship. 6. No systematic effect on the magnitude or onset of the ‘extra’ VO2 was found in relation to pedalling rate, which suggests that it is not related to the pattern of motor unit recruitment in any simple way.

Anthony Sargeant reviews the effect of fatigue and temperature on human muscle power

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In this review based on a Key Note Lecture to a Dutch Physiological Society Symposium Tony Sargeant explains how human muscle power is affected by changes in muscle temperature and by fatigue. Importantly that the magnitude of changes depends on the speed of the muscle contraction generating power and the muscle fibre types present in the muscles.
International Journal of Sports Medicine
Int J Sports Med. 1994 Apr;15(3):116-121

In human locomotion the ability to generate and sustain power output is of fundamental importance. This review examines the implications for power output of having variability in the metabolic and contractile properties within the population of muscle fibres which comprise the major locomotory muscles. Reference is made to studies using an isokinetic cycle ergometer by which the global power/velocity relationship for the leg extensor muscles can be determined.

The data from these studies are examined in the light of the force velocity characteristics of human type I and type II muscle fibres. The ‘plasticity’ of fibre properties is discussed with reference to the ‘acute’ changes elicited by exercise induced fatigue and changes in muscle temperature and ‘chronic’ changes occurring following intensive training and ageing

Effect of pre-stretching muscle on fatigue

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European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1991;62(4):268-273

In activities such as running, many muscles of the lower extremities appear to be actively stretched before they are allowed to shorten. In this study we investigated the effect of an active pre-stretch on the fatigability of muscles. Thus muscle contractions were compared in which shortening was preceded by an active isometric phase or by an active stretch.

Rat medial gastrocnemius muscle-tendon complexes (with arrested blood flow) performed a series of ten repeated contractions (1.s-1) with either an active stretch or an isometric phase preceding the shortening. Contraction duration (0.45 s), and shortening duration (0.3 s), distance (6 mm) and velocity (20 mm.s-1) were the same in both types of contraction. Work output during the ten shortening phases was approximately 40% higher in the contractions with an active pre-stretch; in contrast, high-energy phosphate utilization was similar. Over the ten repeated contractions reduction of work output during the shortening phases of both types of contraction was similar in absolute terms (approx. 9.5 mJ). It is suggested that all the extra work performed during the shortening phases after a pre-stretch originated from sources other than cross-bridge cycling, which are hardly affected by fatigue. However, reduction of work output in relative terms, which is how the reduction is often expressed in voluntary exercise, was less after a pre-stretch (26% vs 32%), giving the impression of protection against fatigue by an active pre-stretch.

Effects of high frquency stimulation on muscle power

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Research carried out by Fabio Abbate as part of his PhD which was supervised by Anthony Sargeant and Arnold de Haan.
Journal of Applied Physiology
J Appl Physiol. 2000 Jan;88(1):35-40.

Abstract: The effects of high-frequency initial pulses (HFIP) and posttetanic potentiation on mechanical power output during concentric contractions were examined in the in situ medial gastrocnemius of the rat with an intact origin on the femur and blood supply. Stimulation of the muscle was performed via the severed sciatic nerve. In the experiments, HFIP or the potentiating tetanus was followed by a stimulation of 80, 120, or 200 Hz.

The results showed that both HFIP and the tetanus increased power output at high contraction velocities (>75 mm/s) when followed by a train of 80 or 120 Hz (200 Hz resulted in no effects). Mechanical power output was increased maximally by HFIP to 120 and 168% by the tetanus. Furthermore, when HFIP or the tetanus were followed by a train of 80 Hz, the peak power in the power-velocity curve tended to be shifted to a higher velocity.

Fatigue causes changes in muscle force and power velocity relationships in muscle

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The data for this research was collected in the Academic Medical Centre of the University of Amsterdam using an experimental model developed by Arnold de Haan who was a PhD student of  Professor Anthony Sargeant. The collaboration with Professor David A Jones was central to the design and interpretations of this study.
Pflugers Archiv
Pflugers Arch. 1989 Feb;413(4):422-8

The force-velocity characteristics of rat medial gastrocnemius muscle have been determined by measuring the force sustained during constant velocity releases of the muscle stimulated in situ at an ambient temperature of 26 degrees C. The velocity of unloaded shortening was determined using the “slack” test and rate of relaxation from the half time of force loss at the end of stimulation. Measurements were first made on fresh muscles using short contractions and then during a series which consisted of a 15 s contraction (fatigued muscle), followed by 15 min recovery and a 1 s contraction (recovered muscle).

After a 5 min recovery period the sequence was repeated. Comparison was made between the fatigued and recovered state in each preparation in order to allow for any change in the preparation during the course of the experiment. After 15 s contraction the fatigued muscles showed a marked reduction in all parameters measured. In fatigued muscles the isometric force fell to 48 +/- 15% (mean +/- SD) and there was a decrease in maximum velocity of shortening to 66%. These changes in the force-velocity relationship were accompanied by slowing of relaxation so that the half time of relaxation nearly doubled. The consequence of these changes was that the maximum power output was reduced by a much greater extent than was the isometric force (75% vs. 52%). It is suggested that the changes in force-velocity characteristics reflect a reduction in cross-bridge cycling in fatigued muscle

The effect of age on muscle performance

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Research into the effects of ageing on muscle function. This work was carried out by Arnold de Haan (later Professor) as part of his PhD supervised by Professor Anthony Sargeant.

Changes in isometric force, power output and relaxation rate have been measured during repetitive tetanic contractions in 2 groups of rats of different ages. During the first 5 contractions there were no differences between a young and mature group. In contrast to isometric force production, which decreased about 3% per contraction, power output initially increased to 108% of the power output in the first contraction.

A greater reduction in power output and relaxation rate after the 5th contraction indicated a greater reduction of the cross-bridge cycling rate in the younger rats. ATP, phosphocreatine and lactate concentrations after the last contraction were not different between the age-groups. In contrast IMP production, which has been suggested may play a regulatory role during fatigue was twice as high in the young rats. Judged by isometric force production there is no age-related difference in fatiguability. However, profound differences were observed in power output, which indicates that quantification of fatigue as a loss of isometric force may be seriously misleading when considering the functional status of the muscle for normal dynamic contractions.