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biceps femoris (BF), lateralis gastrocnemius (GL), and tibialis anterior (TA) was recorded before, during, and after the test. EMG analysis included RMS and ∆%MPF determination. Results The values of the calculated anaerobic parameters were: maximum anaerobic power 2163±787 W, relative anaerobic power 5.7±1.4 W/kg, total anaerobic power 1454±466 kg-m/min and coefficient of anaerobic fatigue
55.9±16.9 %. Heart rate values (bmp) were: during warm-up - 160±24, end of test - 170±11, and recovery - 180±15. Lactate levels increased from 2.1±0.7 to 11.0±2.3 mmol/l, while glucose levels remained statistically unchanged (4.5±0.9 to 4.2±0.6). RMS values (normalized) at the beginning and at the end of the test were as follows: VL) 1.19±0.37 and 1.25±0.52; RF) 1.28±0.19 and 1.46±0.39; ST) 1.17±0.17 and 0.99±0.34; BF) 1.12±0.18 and 1.16±0.51; GL) 1.11±0.17 and 0.83±0.17; and TA) 0.95±0.16 and 0.96±0.34. ∆%MPF values were: VL) ±12.7; RF) +0.9±21.9; SM) -7.4±4.2; BF) -12.5±11.8; GL) -3.6±10.6; TA) +7.9±18.4 %. Discussion The results demonstrate a low anaerobic performance of the tested subjects. The fact that heart rate values rise significantly after the test indicates oxygen debt which is common for anaerobic tests (Weinstein et al., 1998). The significant change in lactate concentration (p=0.002) clearly shows the metabolic origin of fatigue under the tested conditions, although glucose levels reveal a lack of exercise-induced hypoglycemia. Moreover, no significant changes occurred in RMS and MPF (Gerdle et al., 2000, Öberg, 1995) showing that the neuromuscular fatigue is not a limiting factor for performance. References Gerdle B, Larsson B, Karlsson S. (2000). J Electromyogr Kinesiol, 10, 225-232. Öberg T. (1995). J Electromyogr Kinesiol, 5 (4), 239-243. Weinstein Y, Bediz C, Dotan R, Falk B (1998). Med Sci Sports Exerc, 30 (9), 1456-1460. Acknowledgement. This research was supported by the Internal Funding of Regulation 9 of South-West University projects, group B (YMC(H)A).
NEUROMUSCULAR FATIGUE INDUCED BY REPEATED WINGATE TESTSPlace, N., Girard, S., Ivarsson, N., Cheng, A.J., Neyroud, D., Mekideche, A., Truffert, A., Westerblad, H.
University of Geneva Introduction It has recently been suggested that leaky ryanodine receptor (RyR) channels (Ca2+ release channel in the skeletal muscle) might account for the reduced force generating capacity (i.e. muscle fatigue) after prolonged exercise in humans (Bellinger et al. 2008).
As peripheral fatigue predominates after high intensity exercise (Place et al. 2009), the present study was designed to test the hypothesis that muscle fatigue following a strenuous, high intensity exercise, will be mainly of peripheral origin, because of altered RyR function.
Methods Eleven healthy males (27±7 yrs, VO2max 52 ± 8 ml.min-1.kg-1) were recruited to perform 6 Wingate tests (duration 30 s, 0.7 N.m.kg-1) on a cycle ergometer, with 4 min recovery between each repetition. Neuromuscular function of the dominant quadriceps muscle was investigated before and immediately after exercise and consisted in measurement of maximal voluntary contraction (MVC) force, voluntary activation level (VAL, twitch interpolation technique), M-wave properties of the superficial knee extensors as well as potentiated doublet amplitude at 100 Hz (PS100). During neuromuscular testings, subjects were seated on a chair equipped with a force transducer with a knee angle of 90° and supramaximal electrical stimuli were delivered over the femoral nerve. A muscle biopsy was collected from the non-dominant vastus lateralis muscle before and about 10 min after the last Wingate test to analyse eventual changes at the RyR level. Results MVC force was considerably reduced after the repeated Wingate tests (-40.8 ± 5.2%, P0.01). A small but significant reduction in VAL was also observed (-7.3% ± 3.7%, P0.05). PS100 was decreased by 38.6 ± 7.6%, with only minor changes in M-wave properties for vastus lateralis muscle. Muscle biopsies are in the process of analysis. Conclusion This exercise induced considerable muscle fatigue, as evidenced by the large decrease in MVC force. Although VAL -common index of central fatigue- slightly decreased, the large reduction in PS100 seems to indicate that peripheral (muscular) mechanisms mainly account for the impaired maximal force generating capacity. Further, as muscle excitability seems to be relatively well preserved after the exercise, as revealed by the M-wave properties, it seems that processes distal to muscle action potential were impaired (Place et al. 2009). We hypothesize that impaired RyR function, resulting in impaired Ca2+ handling, explains our findings. The anaylsis of muscle samples will allow to test our hypothesis shortly.
References Place et al. Clin Exp Pharmacol Physiol 36(3):334-9, 2009 Bellinger et al. Proc Natl Acad Sci 105(6):2198-202, 2008
FUNCTION OF THE VASTUS LATERALIS MUSCLE FIBERS DURING A RAPID KNEE EXTENSIONOgiso, K., Naruse, K.
Kogakkan University Introduction Shortening of the muscle fibers and increase in pennation angle (PA) contract the pennate muscle. Force generated by the muscles is transmitted to the tendons and finally attain a motor task by rotating the joints. However, the muscle fiber behavior does not seem to be uniform during the contraction, because irregular filament overlaps (Brown and Hill, 1991; Edman and Tsuchiya, 1996), regional differences in strain of the aponeurosis (Kinugasa et al., 2008) and asymmetry in fascicle cross-section deformation (Kinugasa et al., 2012) have been observed. Unexpected and rapid movement we often experience may make the muscle fiber contraction more irregular. The present study was designed to examine function of the vastus lateralis muscle fibers (VL) during a rapid maximal knee extension. Methods Eighteen male subjects performed a 10-consecutive isokinetic knee extension (90 deg/s) that comprised 7 passive and 3 maximal voluntary contractions (MVC) twice. They were asked to relax their muscles and exert MVC as quickly as possible only when a light turned on at 60 deg of the knee joint angle (0 deg = full extension) in the 3rd, 6th and 9th repetitions (C1) or 3 times in random order (C2). VL-EMG activity was monitored to check relaxation before the light stimulus. A point (P) where a fascicle arose from the deep aponeurosis and PA were measured on ultrasonic images of VL. Results The time course of active shortening after the light stimulus was different from that of passive shortening. PA and muscle thickness sharply increased about 200ms after the light stimulus in active shortening, especially near point P. The increase in PA was significantly larger in C1 than in C2. Premotor reaction time, electromechanical delay and total reaction time were also significantly shorter in C1 than in C2. Discussion VL contracted at MVC just as if the fascicle bit on the deep aponeurosis tightly, which was made quicker and larger by expecting the light stimulus. This markedly differs from the fascicle movement during isometric and slow isotonic contractions. Conduction velocity of the action potential becomes gradually slow near the tendon (Iwata, 1983; Kusama, 1987). Therefore, the biting movement might result from wave summation near the deep aponeurosis, which might lead to irregular behavior of the muscle-tendon complex. This may explain why most of muscle strain injuries occur at myotendinous junction (Garrett, 1990). References Brown LM, Hill L (1991) J Muscle Res Cell Motil, 12(2): 171-182. Edman KAP, Tsuchiya T (1996) J Physiol, 490(1): 191-205. Garrett WE (1990) Med Sci Sports Exerc, 22(4): 436-443. Iwata K (1983) Chiba Med J, 59: 171-179. Kinugasa
R et al. (2012) J Appl Physiol, 112(3): 463-470. Kinugasa R et al. (2008) J Appl Physiol, 105: 1312–1320. Kusama T (1987) Chiba Med J, 63:
10:20 - 11:50 Invited symposia IS-BN03 Biomechanical human-environment interaction
THE EFFECT OF DIFFERENT SKI-SNOW INTERACTION MODES ON THE HUMAN BODYKröll, J., Spörri, J., Müller, E., Schwameder, H.
University of Salzburg In order to turn and regulate speed, a skier must manipulate the orientation and loading pattern of the skis to generate adequate reaction forces from the snow surface. Therefore, a deeper understanding of this ski-snow interaction is an essential component for equipment development. The overall ski performance is primarily affected by the side cut and the torsional and bending stiffness of the skis.
Consequently the tuning of these properties may be essential for performance, comfort and injury prevention issues. The principle influence of different ski-snow interaction modes can be demonstrated by theoretical considerations. Hence, the first part of the talk will deal with theoretical models of ski-snow interaction mechanics which already have been described and tested using numerical simulations and physical models. However those models only superficially account for the effect of different Ski-Snow interaction modes on the human body. In order to better understand the effect of different ski-snow interaction modes on the human body it is necessary to consider experimental data from in vivo field studies as well. Therefore, empirical data from an intervention study will then be presented. The aim of this study was to quantify the evolution of total external and internal loads of elite athletes arising from different ski equipment designs under simulated competition conditions. Based on the recent changes of FIS equipment rules, ski side cut radii with 27m (GS 27) were compared against ski side cut radii with 35m (GS 35). Ski ground reaction forces (Pedar Insoles), kinematics (IMU Sensors) and muscle activity (EMG) were determined simultaneously. Comparing GS35 and GS27, force distribution alters forces in a manner that the outside leg forces decrease substantially with GS35 towards the end of the turn. However, an opposite behavior was observed on the inside leg where forces increased slightly at the end of the turn. From a neuromuscular perspective, one would expect that the alterations in external load are directly reflected in the leg extension muscle group. However, the neuromuscular alterations are only partially linked to external load, but in some cases are closely linked to functional aspects of the used ski. This can be observed in the tibialis anterior muscle where an increased activity on both inside leg and outside leg can be observed during the GS35 trial which is seen as “less functional” in a carving ski function. For the final part of the talk, the influence of the theoretical and in vivo approaches will be related along with the potential and limitations to our ski-snow interaction understanding.
ESTIMATING AND ADJUSTING FOR EFFECTS OF ENVIRONMENTAL FACTORS IN SPORT RESEARCHHopkins, W.G.1, Hume, P.A.1, Hollings, S.C.1, Hamlin, M.J.2, Spencer, M.3 1: AUT University (Auckland, New Zealand). 2: Lincoln University (Christchurch, New Zealand). 3: Norwegian School of Sport Sciences (Oslo, Norway).
Environmental and other venue-related factors (e.g., weather, surface conditions, altitude) can have important effects on performance, injury and related dependent variables. As such, they are also nuisance variables that modify the dependent variable in studies of other factors affecting performance or injury. Appropriate inclusion of environmental factors in a linear model not only provides estimates of the effects of the environment but also improves the precision of estimates of other effects and adjusts them to chosen values of the environmental factors. When the environment differs between but not within athletes (e.g., single performances by different athletes at different venues), the effects of environmental differences can be estimated with a covariate in a traditional ANOVA linear model. Such models require hundreds of athletes on each level of the environmental variable to estimate effects with sufficient precision for adjusting outcomes of the main dependent variable. When the environment differs within athletes (e.g., multiple performances by the same athletes at different venues), the changes in the environment are represented by a covariate that changes within each subject. Such within-subject covariates cannot be included in ANOVA models, but mixed linear models allow for them and thereby usually provide adequate precision with smaller sample sizes. There are several options to specify covariates in linear models. A simple linear effect is specified with a numeric covariate. A potentially non-linear effect should be investigated by parsing the covariate either into quantiles or other appropriate subgroups, then specifying the covariate as a nominal variable and estimating the means and differences between means of the different levels. The covariate can also be specified as a quadratic or higher-order polynomial, especially when the aim is to estimate the value of the covariate that maximizes or minimizes the main dependent variable. It is also possible to specify two discontinuous linear effects (e.g., one slope over a low range and another over a high range of an environmental variable) by interacting dummy variables with covariates representing the two linear effects; the transition value of the covariate can then be found by iterative analysis. Non-linear mixed models are another option with such data. Some of these analyses will be illustrated with data from recent studies of the effects of environment on performance of track-and-field athletes and downhill skiers.