• Gert-Peter Brüggeman


INTRODUCTION -Several studies have indicated changes in lower leg kinematics occurring in different stages of endurance activities (eg. Hamill et al., 1992; Williams et al., 1991). Others have found differences in rear foot motion in over ground or treadmill running before and after exhaustion treatments (Van Gheluwe et al., 1995; Brüggemann et al., 1995) Few relevant data are available on kinetic data. Brüggemann et al. (1994) reported a decreased impact force during endurance running at constant running speed sometimes accompanied by an increase in pronation during the early stance phase. Nicol et al. (1991) found influences of fatigue upon neuromuscular performance by investigating power in lower leg activities during short stretchshortening cycles before, during and after an marathon. It can be speculated that muscular and neural fatigue lead to significant changes in muscular activation patterns, muscle stiffness and possibly the storage capacity of elastic energy of the muscle-tendon complex. From this perspective most studies attempting to understand footwear functions with the aim of impact force cushioning at touchdown and control of rearfoot motion must be discussed with some reservation when applied to fatiguing activities. Previous studies concerning rearfoot motion, ground reaction forces or insole pressure distribution during sport activities have been based upon the assumption of constant metabolic circumstances and stable neuromuscular control. Therefore, the purpose of the paper was 10 summarize the present state of knowledge and to investigate the influence of different stages of peripheral (or muscular) and central fatigue on micro-control mechanisms and lower extremity function during running. A short review of literature will be supplemented by current data from our own studies METHODS –A series of experiments was designed to determine the influence of muscular and central fatigue on lower extremity function during running The first study analysed the influence of local muscular fatigue of the shank muscles on lower extremity function during running. In a second experiment fatigue was induced by running and lower extremity function was examined. Therefore, running speed and mechanical properties of the shoes remained constant in both studies, whereas the different stages of fatigue were used as experimental variables. Study no.1: After 5 minutes of adaptation to treadmill running at 35 m/s kinematic, kinetic and EMG data were obtained from the ten subjects. Subsequently the shank muscles were locally loaded using a specially designed training device. Immediately after the treatment the subjects entered the treadrnill again and were examined for a second time Study no.2: Ten subjects ran 45 minutes on the instrumented treadmill at a speed of 3.0 m/s Not all subjects completed the 45 minutes run therefore, complete data sets for 35 minutes running were available for further analysis. Data acquisition Vertical ground reaellon forces were measured using an instrumented treadmill (GaitKinetics) which permitted individual registration of the ground reaction forces of both feet. An inshoe goniometer registered the rearfoot angle in relation to the shank. EMG signals from the m. triceps surae, the m. tib. ant.the m. peroneus longus, the m. vastus lat. and the m biceps femoris were preamplified and registered simultaneously with the force and angle data RESULTS AND DISCUSSION -Study no.1 The matching time intervals indicated a longer contact phase and a trend to a later occurrence of impact peak force induced by fatigue. The ß (rearfoot) angles at touchdown increased far all subjects with one exception. The same result applied to the change of the angle ß from touchdown to its maximum Fatiguing m. tib .ant and m. peraneus longus seemed to correspond to a stiffness reduction of the musculature supporting the ankle joint and thus to a decrease of impact peak force. In addition the ß values at touchdown indicated decreased muscular control prior to heelstrike following the treatment This resulted in an increased range of motion. The EMG recordings reported a time shift of muscle activation for all analysed muscles to the right Study no. 2 In a comparison of subjects and different stages of running, maximum impact peak of the ground reaction force was normalized to the mean of the second data collection executed 7 minutes after adaptation to the treadmill running .The data indicated a greater peak force in the first phase of running. This was combined with a small decrease of the time to peak. After this first adaptation the peak forces increased in relation 10 running or loading time. All mean values were significantly different from the second measurement. The decrease in the maximum impact peak was combined with an increase of time to peak. The rearfoot angle ß at touchdown and the time to maximum ß generally changed after approximately 15 minutes of running. The rapid increase in the touchdown ß angle indicated a significant disturbance in the touchdown action of the foot. The increased time to maximum angle may be interpreted as a fatigue induced effect of the ankle stabilising medio-lateral structures. Both changes could be observed simultaneously. The MPF of the m. triceps surae decreased significantly after the second data collection. This indicated the fatigue of this muscle which might be correlated to the above discussed decrease of the pushoff force. In the 150 ms interval prior to touchdown the MPF of the m. vastus lateralis decreased after approximalely 7 minutes of running. Minimum values occured after approximately 12 minutes of running. This coincided with the above discussed changes of the rearfoot angle ß patterns. The changes of the MPF of the m. vastus lateralis during the stance phase showed a very similar pattern as during preactivation. This indicated a substantial fatigue of the knee extensor musculature after approximately 12 to 15 minutes of running in a group of medium trained joggers. CONCLUSION -Muscular fatigue was induced in both experiments and detected by an MPF decrease. Muscular fatigue was related to a decrease of impact peak forces and to changes in rearfoot kinematics. Therefore, it appears that stiffness regulation is affected by fatigue. L1TERATUREBrüggemann, G.-P., and Arndt, A.N. (1994). Fatigue and lower extremity function. Abstract, 8th Congress CSB, Calgary. Brüggemann, G.-P, Arndt, AN, Kersting, U.G. and Knicker, AJ. (1995). Influence of fatigue on impact force and rearfoot motion during running. Abstract, XVth Congress of the ISB. Jyväskylä. Hamill, J., Bates, B.T. and Holt, KG. (1992). Timing of lower extremity joint actions during treadmill running. Med. Sei. Sport and Exercise, 24 (7); 807-813. Nicol, C, Komi, P.V. and Marconnet, P. (1991). Fatigue effects of marathon running on neuromuscular performance. Scand. J. Med. Sei. Sports, 1; 10-17. Van Gheluwe, B, Kopriva, N. and Madsen, C. (1995). Rearfoot motion prior to volitional exhaustion. Abstract, XVth Congress of the ISB. Jyväskylä. Williams, K.R, Snow, Rand Agruss, C. (1991). Changes in distance running kinematics with fatigue. Int J. Sport. Biom, 7; 138-162. 48