Neuromuscular fatigue and mechanical alterations in intermittent activities: applications to racket sports
On December 1st 2006, Olivier Girard presented his Ph.D. thesis titled Neuromuscular fatigue and mechanical alterations in intermittent activities: applications to racket sports, concluding five intensive years (including a masters degree on the same topic) of study on the analysis of racket sport determinants at the Faculty of Sports Science in Montpellier in the South of France.
Summary of the Thesis:
The main objective of this thesis was to analyse the mechanical alterations under fatigue in racket sports (mainly in tennis but also in squash). Three approaches (physiological, neuro-physiological and biomechanical) were used:
1. Regarding the physiological approach, metabolic responses to competition in racket sports players were studied in order to design sport-specific tests. The aim of the first study was to describe the characteristics of squash (temporal structure) and to determine the energy requirements (metabolic and cardiorespiratory) during test matches in elite players. The purposes of studies 2 and 3 were i) to develop a squash (study 2) and a tennis (study 3) specific incremental fitness test which included some elements of game play; and ii) to compare physiological responses recorded during these field procedures with those observed during an incremental treadmill test. The results have shown that although cardiorespiratory variables were not different at submaximal intensities between the two tests, maximal oxygen uptake values derived from laboratory measurements were underestimated. Using field testing in addition to treadmill testing provides a better measurement of a players individual fitness level and may be routinely used to accurately prescribe appropriate aerobic exercise training.
2. The neuro-physiological approach aimed to explore mechanisms underlying alterations in muscle function induced by prolonged intermittent activities such as tennis. Changes in exercise characteristics, maximal voluntary contraction and explosive strength during a long duration (three hour) tennis match play have been examined (study 4). Progressive reductions in maximal voluntary strength and leg stiffness highly correlated with increases in perceived exertion and muscle soreness were observed throughout a three hour tennis match, whereas explosive strength was maintained and decreased only after the match. In study 5, the time course of impairment in neural and contractile processes during prolonged tennis playing (three hours) has been investigated in order to determine the origin (central and/or peripheral) of strength loss. The main results indicated that central activation failure and alterations in excitation-contraction coupling are probable mechanisms contributing to the moderate impairment of the neuromuscular function during prolonged tennis playing. The aim of study 6 was to precise the time course of alteration in neural process (spinal loop properties). It was concluded that the decrease in torque induced by this type of long duration intermittent activity is specifically modulated by neural mechanisms at the spinal level.
3. The biomechanical approach was designed to investigate lower extremities activity in tennis, notably during the serve. The purpose of study 7 was to examine lower-limb activity (EMG, ground reaction forces) in tennis players of different performance levels during the power serve. The results demonstrated that the vertical forces and co-ordination in lower extremities during the tennis serve were different between players of different skill levels, which may partly explain the difference in serve efficiency. The use of the joint immobilisation method (restricted knee motion) was used as a paradigm for interrupting the normal mechanisms used by players to perform serve and therefore discuss the role of the lower extremities in generating high-speed serves (study 8). The aim of study 9 was to determine if decline in stroke quality of the tennis serve under fatigue (after a 2 h 30 min match play) would be related to changes in i) the co-ordination sequence of body segments and ii) the magnitude of the ground reaction forces and EMG signals in the lower extremities. Finally, the aim of study 10 was two-fold: compare in-shoe loading patterns between different i) tennis serve conditions and ii) tennis-specific displacements performed alternatively on two playing surfaces (clay and Greenset). The results indicated that foot loading is significantly affected by service technique and ground type surface. In particular, the relative load on the medial and lateral mid-foot were higher on clay than on Greenset. In contrast, the Greenset condition induced significantly higher relative loads in the hallux and lesser toes areas compared to clay.
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|Subjects:||sports game tennis table tennis squash badminton sport physiology neurophysiology fatigue|
|Notations:||biological and medical sciences sport games|
|Published in:||Medicine and Science in Tennis|
|Document types:||electronical journal