The electrical stimulation of leg muscles (including FES) of people with Spinal cord injury will be affected by the temperature of the muscle

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This research publication formed part of the PhD thesis of H.L. Gerrits who was directed by a team of colleagues from the Vrije Universiteit of Amsterdam headed by Professor Anthony J Sargeant and Professor Maria Hopman from the Radboud University Nijmegen. The paper shows that (the typically) low muscle temperatures in the limbs of people with spinal cord injury will change the the contractile properties of the muscles when functional electrical stimulation is applied or the muscle properties are assessed in the laboratory.

Influence of muscle temperature on the contractile properties of the quadriceps muscle in humans with spinal cord injury

H. L. GERRITS, ARNOLD DE HAAN, MARIA T HOPMAN, LUC H. V. VAN DER WOUDE, ANTHONY J SARGEANT.

Clinical Science
Clin Sci (Lond). 2000 Jan;98(1):31-8
Abstract
Low muscle temperature in paralysed muscles of individuals with spinal cord injury may affect the contractile properties of these muscles. The present study was therefore undertaken to assess the effects of increased muscle temperature on the isometric contractile properties of electrically stimulated paralysed quadriceps muscles. When muscle temperature at a depth of 3 cm was increased from approximately 32 degrees C to approximately 36 degrees C by ultra-short-wave application, the half-relaxation time shortened and low-frequency force responses became less fused, but the maximal rate of increase in force remained unchanged. Heating had no effect upon either force decline or slowing of relaxation during fatiguing contractions. The force-frequency relationship of the paralysed quadriceps muscle was shifted to the right after the muscle was heated. Despite this shift, however, the relationship still resembled that in muscles of non-paralysed individuals, probably due to the unexplained high twitch forces. These results indicate that reduced muscle temperature in spinal-cord-injured individuals may lead to an underestimation of the changes in contractile properties in terms of relaxation rate or the degree of fusion with low-frequency stimulation. In addition, the force-frequency relationship of paralysed muscles does not accurately reflect the magnitude of these changes, even when the muscle is heated, and should therefore be treated with caution.
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Prior activation can change the maximum power generated by skeletal muscle

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Fabio Abbate was a PhD student working under the direction of Professor Anthony J Sargeant in Amsterdam. This was one of a number of research papers published in eminent scientific journals which formed part of Fabio Abbate’s PhD thesis successfully submitted at the Vrije Universiteit of Amsterdam.

Effects of high-frequency initial pulses and posttetanic potentiation on power output of skeletal muscle

F. Abbate, Anthony J Sargeant, P. W. L. Verdijk, 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.

Optimum pedalling rates in cycling

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The data for this research publication was collected in Amsterdam by Jerzy Zoladz and Arno Rademaker working under the supervision of Professor Anthony J Sargeant. The concept of optimum movement frequencies in human locomotion had been a long standing interest of Tony Sargeant’s and the results from this study build on earlier studies. It is concluded that choosing a high pedalling rate (around 100 revs/min) when performing high intensity cycling exercise may be beneficial since it provides greater reserve in power generating capability and this may be advantageous to the muscle in terms of resisting fatigue.

Human muscle power generating capability during cycling at different pedalling rates

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

Experimental Physiology

Exp Physiol. 2000 Jan;85(1):117-24

Abstract
The effect of different pedalling rates (40, 60, 80, 100 and 120 rev min-1) on power generating capability, oxygen uptake (O2) and blood lactate concentration [La]b during incremental tests was studied in seven subjects. No significant differences in O2,max were found (mean +/- S.D., 5.31 +/- 0.13 l min-1). The final external power output delivered to the ergometer during incremental tests (PI,max) was not significantly different when cycling at 60, 80 or 100 rev min-1 (366 +/- 5 W). A significant decrease in PI,max of 60 W was observed at 40 and 120 rev min-1 compared with 60 and 100 rev min-1, respectively (P < 0.01). At 120 rev min-1 there was also a pronounced upward shift of the O2-power output (O2-P) relationship. At 50 W O2 between 80 and 100 rev min-1 amounted to +0.43 l min-1 but to +0.87 l min-1 between 100 and 120 rev min-1. The power output corresponding to 2 and 4 mmol l-1 blood lactate concentration (P[La]2 and P[La]4 ) was also significantly lower (> 50 W) at 120 rev min-1 (P < 0.01) while pedalling at 40, 60, 80 and 100 rev min-1 showed no significant difference. The maximal peak power output (PM, max) during 10 s sprints increased with pedalling rate up to 100 rev min-1. Our study indicates that with increasing pedalling rate the reserves in power generating capability increase, as illustrated by the PI,max/PM,max ratio (54.8, 44.8, 38.1, 34.6, 29.2%), the P[La]4/PM,max ratio (50.4, 38.9, 31.0, 27.7, 22.9%) and the P[La]2/PM,max ratio (42.8, 33.5, 25.6, 23.1, 15.6%) increases.
Taking into consideration the O2,max, the PI,max and the reserve in power generating capability we concluded that choosing a high pedalling rate when performing high intensity cycling exercise may be beneficial since it provides greater reserve in power generating capability and this may be advantageous to the muscle in terms of resisting fatigue. However, beyond 100 rev min-1 there is a decrease in external power that can be delivered for an given O2 with an associated earlier onset of metabolic acidosis and clearly this will be disadvantageous for sustained high intensity exercise.

Review of research into muscle power and fatigue

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Anthony Sargeant and David A Jones wrote this invited review for an important book on muscle fatigue edited by Simon Gandevia and others

The significance of motor unit variability in sustaining mechanical output of muscle

Anthony J Sargeant and David A Jones

Advances in Experimental Medicine and Biology
Adv Exp Med Biol. 1995;384:323-38
Neuromuscular function and fatigue have been studied using a wide variety of preparations. These range from sections of single fibers from which the cell membrane has been removed to whole muscles or groups of muscles acting about a joint in the intact animal. Each type of preparation has its merits and limitations. There is no ideal preparation; rather the question to be answered will determine the most appropriate model in each case and sometimes a combination of approaches will be needed. In particular, it is important to understand how the mechanical output of whole muscle can be sustained to meet the demands of a task and to take into account the organized variability of the constituent motor units.

Age Related Changes in Muscle Power

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Margriet Lodder completed this work in Amsterdam as part of her PhD research under the direction of Professor Anthony Sargeant
Effect of growth on efficiency and fatigue in extensor digitorum longus muscle of the rat
Margriet A Lodder

Arnold de Haan

Anthony J Sargeant.

European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1994;69(5):429-434
The effect of growth on work output, energy consumption and efficiency during repetitive dynamic contractions was determined using extensor digitorum longus muscles of 40-, 60-, 120- and 700-day-old male Wistar rats. When work output of each contraction was normalized to the work output of the first contraction it was found that work output initially increased over the first 10-20 contractions by approximately 8% in each age group. Thereafter a faster decrease in work output was found in the youngest group (approximately 2% each contraction) compared to the older groups (approximately 0.7% each contraction). After 40 contractions the reduction in work output was significantly different only between the youngest group and the two oldest groups (-30% vs -5%). These differences in fatigue were not associated with differences in adenosine 5′-triphosphate and phosphocreatine concentrations or in lactate production. Total work output and high-energy phosphate consumption increased by approximately 555% and 380% from age 40 to 120 days, respectively. Consequently, efficiency was significantly higher (approximately 32%) in the older groups compared to 40-day-old animals. Normalized for muscle mass, mean rate of high-energy phosphate consumption was similar in all groups whereas mean power output was significantly lower in the youngest group (approximately 46%). Thus, the difference in efficiency between the young and the other groups may be attributed to a lower external power production in the youngest group rather than changes in energy turnover

Fatigue during cycling is related to pedalling rate

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Research carried out by Anita Beelen under the direction of Anthony Sargeant extended his interest in short-term muscle power output (sometimes referred to as anaerobic power). In cycling it can be seen that the degree of fatigue from prior exercise is greater when measured at higher pedalling rates. This is consistent with fatigue inducing prior exercise reducing the power generation of the faster of the most fatigue sensitive muscle fibres in the mixed human leg muscles.
European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1993;66(2):102-107

The effect of prior submaximal exercise performed at two different pedalling frequencies, 60 and 120 rev.min-1, on maximal short-term power output (STPO) was investigated in seven male subjects during cycling exercise on an isokinetic cycle ergometer. Exercise of 6-min duration at a power output equivalent to 92 (SD 5)% maximal oxygen uptake (VO2max), whether performed at a pedalling frequency of 60 or 120 rev.min-1, reduced maximal STPO generated at 120 rev.min-1 to a much greater extent than maximal STPO at 60 rev.min-1. After 6-min submaximal exercise at 60 rev.min-1 mean reductions in maximal STPO measured at 120 and 60 rev.min-1 were 27 (SD 11)% and 15 (SD 9)% respectively, and were not significantly different from the reductions after exercise at 120 rev.min-1, 20 (SD 13)% and 5 (SD 9)%, respectively. In addition, we measured the effect of prior exercise performed at the same absolute external mechanical power output [236 (SD 30)W] with pedalling frequencies of 60 and 120 rev.min-1. Although the external power output was the same, the leg forces required (absolute as well as expressed as a proportion of the maximal leg force available at the same velocity) were much higher in prior exercise performed at 60 rev.min-1. Nevertheless, maximal STPO generated at 120 rev.min-1 was reduced after exercise at 120 rev.min-1 [20 (SD 13)%, P < 0.05] whereas no significant reduction in maximal STPO was found after prior exercise at 60 rev.min-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimum wheelchair propulsion techniques

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One of another in the series of practical human physiology studies that Anthony Sargeant supervised as Professor in the Academic Medical Centre of Amsterdam. In this case the data was collected by Luc van der Wooude (now Professor), a dedicated PhD student, under his supervision.
European Journal of Applied Physiology
Eur J Appl Physiol Occup Physiol. 1989;58(6):625-32

To study the effect of different cycle frequencies on cardio-respiratory responses and propulsion technique in hand-rim wheelchair propulsion, experienced wheelchair sportsmen (WS group; n = 6) and non-wheelchair users (NW group; n = 6) performed wheelchair exercise tests on a motor-driven treadmill. The WS group wheeled at velocities of 0.55, 0.83, 1.11 and 1.39 m.s-1 and a slope of 2 degrees. The NW group wheeled at 0.83, 1.11 and 1.39 m.s-1 and a 1 degree slope. In each test, a 3-min period at a freely chosen cycle frequency (FCF: 100%) was followed by four 3-min blocks of paced cycle frequencies at 60%, 80%, 120% and 140% FCF. Effects of both cycle frequency and velocity on physiological and propulsion technique parameters were studied. Analysis of variance showed a significant effect (p less than 0.05) of cycle frequency on oxygen cost and gross mechanical efficiency in both the WS and NW group. This indicated the existence of an optimum cycle frequency which is close to the FCF at any given velocity. The optimum cycle frequency increased with velocity from 0.67 to 1.03 cps over the range studied (p less than 0.05). Oxygen cost was approximately 10% less at 100% FCF than at 60% or 140% FCF. Gross mechanical efficiency for the WS group at 100% FCF was 8.5%, 9.7%, 10.4% and 10.1%, respectively, at the four velocities.(ABSTRACT TRUNCATED AT 250 WORDS)