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Technical University of Munich, Faculty of Sport Science INTRODUCTION Although the phenomenon of residual force enhancement (RFE) is well known and has been systematically observed from single sarcomeres to in vivo human muscles, its relevance for everyday movements performed with submaximal efforts remains unclear. Therefore, the aim of this study was to investigate the idea of RFE being a more effective and energy saving muscular property during an everyday like submaximal multi-joint leg extension. METHODS Subjects (n = 13) performed bilateral isometric (100° knee flexion) and stretch contractions (80-100° knee flexion at 60°/s with subsequent isometric contractions) in a motor driven legpress dynamometer at submaximal efforts of 30% vastus lateralis (VL) EMG (EMG-control) and 30% Fmax (force-control), respectively. Further, subjects performed purely isometric and stretch contractions at 50% force-control until time to failure. External reaction forces were measured by 3D force plates and activity of 9 lower leg muscles was assessed using EMG. Kinematics were analysed by a VICON system and inverse dynamics served for calculating ankle, knee, and hip joint torques. Visual feedback of VL EMG or external reaction force was given to control submaximal efforts. RESULTS For EMG-control we found no differences in VL activity between isometric and stretch contractions but significant RFE at the level of external reaction forces and joint torques.
NEUROMUSCULAR RECRUITMENT AND COMMON DRIVE OF THE KNEE EXTENSORS FOLLOWING ACUTE
ACCENTUATED ECCENTRIC LOADHunter, A.M., Pahar, M., Balshaw, T.G.
University of Stirling Introduction Resistance exercise performed with overload of the eccentric phase (AEL) can lead to superior strength gains compared to constant load (CL) exercise (Hortobagyi et al., 2001). Initially, strength adaptations occur from increases in neural drive (Selvanayagam et al., 2011); therefore, it is possible that acute altered neural responses could contribute to this stimulus. Our aim was to investigate motor unit recruitment and common drive (CD) (motor unit discharge rate) following AEL in comparison to CL protocols at 2 different eccentric velocities (4 or 2 seconds). Methods Ten healthy males attended the laboratory on 4 separate occasions in random order to perform a maximal isometric voluntary contraction (MVC) followed by a 10 second submaximal trapezoid contraction (70% of MVC)(TRAP) during which high density EMG (De Luca and Hostage., 2010) recorded firing rates of motor units from the vastus lateralis (VL). CD was then analysed from the 3-second plateau phase of the TRAP with the greatest reliability. Then, the participants either did CL (2s), AEL (2s), CL (4s) or AEL (4s). AEL and CL consisted of eccentric load at 120% and 85% of 3RM respectively. All conditions consisted of a concentric load of 85% of 3RM which consisted of 3 x 3, and then MVC and TRAP was repeated. Global EMG was also recorded from the VL during these contractions and was normalised to baseline dynamic strength tests. Results For all interventions no alterations where shown in MVC
following exercise, also no differences occurred in concentric velocity between conditions. Normalised EMG amplitude (RMS) was significantly (p0.01) greater in the eccentric phase in AEL vs. CL for both fast (f) and slow (s) contractions (AEL:193.7 + 6.5% f 192.7 + 6% s CL:
145.3 + 5% f 135.4 + 5% s). No differences were observed between conditions for CD. For all conditions peak cross-correlation histogram frequency appeared in the range of 0.6 to 0.7 and no differences were shown for maximum and mean peak cross-correlation coefficients (p 0.05). Discussion Despite the additional load maximal force capacity of the knee extensors was maintained following AEL.
Although there was an increase in motor units recruited during the eccentric phase of AEL there was no alteration in common drive following the intervention. This has therefore demonstrated that AEL increases motor unit recruitment but not in residual common drive in response to a heavier load. Thus, it is likely that neuromuscular responses in the eccentric phase of AEL are responsible for superior adaptations previously reported. References De Luca CJ and Hostage EC. J Neurophysiol 2010;104(2):1034-1046. Hortobagyi T, Devita P, Money J, Barrier J. Med Sci Sports Exerc 2001;33(7):1206-1212. Selvanayagam VS, Riek S, Carroll TJ. J Appl Physiol 2011;111(2):367-375.
ANKLE DESTABILISATION DEVICE FOR INJURY PREVENTION OR REHABILITATION IN SPORTSPaizis, C., Fautrelle, L., Baroudi, A.R., Deley, G., Babault, N.
University of Burgundy Introduction Numerous epidemiological studies demonstrated that lateral ankle sprain (LAS) is a recurrent problem in athletes (Hootman et al. 2007). Further to LAS, residual symptoms could arise and about 70% of the athletes who suffered from acute LAS develop chronic ankle instability (Hertel 2002). At the muscular level, evertor muscles strength is an essential factor in order to ensure ankle stability (Wilkerson et al. 1997). In this study, we proposed to investigate the modulation of the EMG activity of 6 ankle muscles (on the right and left leg) when wearing an ankle destabilisation device (ADD) in different situations. We hypothesized that ADD would significantly modify the amplitude of the EMG pattern of the ankle muscles, especially in peroneal muscles. Methods Twelve healthy active subjects without previous history of neuromuscular disease or acute LAS volunteered for the experiment. Subjects were required to walk forward and backward, on both sides and in circles, with or without the ADD. They were then asked to maintain unipodal equilibrium with a Freeman board. Kinematics and surface electrical activities were recorded on six muscles of both legs, namely the tibialis anterior, peroneus longus, peroneus brevis, gastrocnemius lateralis, gastrocnemius medialis and soleus. EMG activity recorded during each experimental condition was normalized by the EMG activities recorded during a maximal voluntary isometric contraction. Results Electromyographic recordings showed a significantly increased activity during dynamic equilibrium but also when wearing ADD during normal walk forward and backward, circle walking in both directions (P0.05). Discussion Our findings evidenced that walking in different conditions with ADD generates a significant increase in electromyographic activity of tibialis and both peroneus muscles, and therefore suggest that ADD are a valuable resource for functional strength training, sensory-motor rehabilitation and prevention of the ankle injury. References Hootman JM, Dick R, Agel R. (2007). J Athl Train, 42: 311-9. Hertel J (2002). J Athl Train, 37: 364-375 Wilkerson GB, Pinerola JJ, Caturano RW (1997) J Orthop Sports Phys Ther, 26: 78-86.
REDUCED TYPE IA AFFERENT FEEDBACK DOES NOT INFLUENCE QUADRICEPS MAXIMAL AND EXPLOSIVE ISOMETRIC
FORCE PRODUCTION IN MANFry, A., Folland, J.P.
Loughborough University Introduction The role of afferent feedback in maximal motor tasks remains poorly understood. Whilst it has been suggested that a reduced efficacy of the γ-loop following tendon vibration may impair maximal voluntary force, the limited previous studies have been equivocal in their findings. Furthermore, the effect of vibration, and attenuation of the γ-loop, on explosive force production is unknown.
The aim of this study was to investigate the role of afferent feedback in maximum and explosive isometric force production of the quadriceps, using a prolonged tendon vibration to attenuate the Ia afferent-α-motoneuron pathway. Methods Eighteen healthy males (21±2 years) performed a series of voluntary and evoked isometric unilateral knee-extensor contractions pre and post two separate 30-min intervention trials of: infrapatellar tendon vibration (80 Hz) and quiet sitting (control), 7 days apart. Participants performed six explosive and two maximal force contractions to assess volitional function, and supramaximal twitch and octet responses were evoked to assess the contractile properties of the muscle-tendon complex. The efficacy of the Ia afferent-α-motoneuron pathway was determined by assessing the H-reflex (Hmax:Mmax ratio of the vastus medialis) at rest, at the start and end of each series of volitional and evoked contractions, pre and post intervention (i.e. at four time points). Participants remained seated in a strength testing chair throughout the trials, with knee and hip angles of 120° and 105°, respectively. Force was measured via a strain gauge strapped perpendicular to the tibia, and surface EMG was recorded from six sites over the quadriceps and two over the hamstrings. Results Post-intervention Hmax:Mmax was 60% lower in the vibration trial vs. control, and remained 38% lower at the end of the post-intervention measurements (t-test, both P0.01). In contrast, no trial × time interactions were found for either maximum force (ANOVA, P=0.92) or explosive force (at 50, 100 and 150 ms after force onset; ANOVA, all P≥0.36), or their corresponding mean agonist EMG amplitude (ANOVA, all P≥0.23). Evoked responses were also unchanged following vibration (ANOVA, all P≥0.39). Individual Hmax:Mmax depression did not correlate to changes in either maximum or explosive force (Spearman’s Rank, all P≥0.54). Discussion The reduction in H-reflex demonstrated that the vibration stimulus effectively attenuated the homonymous Ia afferent-α-motoneuron pathway for the duration of the post-intervention measurements. However, voluntary maximal and explosive force production remained unchanged. Therefore, Ia afferent feedback does not appear to contribute significantly to either maximal or explosive isometric force production of the quadriceps.
TORQUE-ANGLE RELATIONSHIPS OF THE ELBOW FLEXORS AND EXTENSORS IN HEALTHY FEMALESPencheva, N., Kokova, M., Dencheva, S.
South-West University Introduction The aims of this study are: (1) to obtain knowledge of the isometric torque-angle relationship of the elbow flexors and extensors; (2) to explore the impact of the elbow angle on the neuromuscular activity of the biceps brachii – long head (BB-LH) and triceps brachii – long head (TB-LH) by recording sEMG activity; and (3) to evaluate the correlations between the isometric flexor or extensor torque and RMS of the muscles tested. Methods Maximal isometric torque of flexors and extensors were measured (Biodex System 4) over a wide range of angles (15-150o) in ten females (21.2±1.4 years). Agonistic EMG activity and the level of coactivation for BB-LH and TB-LH were also measured. The curve fitting and statistics were performed by Prism software. Results The isometric torque-angle curves of flexors and extensors were modeled with 4th order polynomial function. The maximal torque of flexors (28.0±7.5 Nm) was generated at 90-105o position, while that of extensors (28.9±6.7 Nm) at 60-75o. The flexors/extensors torque ratio was lower, equal or higher than 100 % in the angular positions of 15-75o, 90o or 105-150o respectively. Agonistic EMG activity level of the BB-LH, as RMS, was correlated to measured torque of flexors, within the range of 75-150o (Spearman’s r=0.82), while that of TB-LH did not correlate with extensor’s torque.
The antagonist activity for both muscles was low and did not result angle-dependent. Discussion In this study we found that the skew part (tail) of the non-linear, asymmetric torque-angle curve of flexors is situated in the left part of the measured range, while that of extensors, in the right one. These findings and the respective agonistic RMS-angle curves for BB-LH and TB-LH, seem to correspond at some extent to the force-length and to the moment arm-angle relationships (Ada et al., 2003; Pinter et al., 2010). However, the lack of correlation between extensor torque and activity of TB-LH can be explained by lower isometric functional capacity of the long head, which according to Murray еt al. (2000) has shorter moment arm, as compared with that of BB-LH. Although, we found low and independent of elbow angle antagonistic activity of both muscles, it is hard to predict the size of crosstalk and the degree of underestimation of the maximal elbow torque, especially for extensors. References Ada L, Canning CG, Low ShL. (2003). Brain, 126, 724-731. Murray WM, Buchanan ThS,
Delp SL. (2000). J Biomech, 33 (8), 943-952. Pinter IJ, Robbert MF, van Soest AJ, Smeets JB. (2010). J Electromyog Kinesiol, 20, 923-931.
Acknowledgement. The research was supported by the Internal Funding of Regulation 9 of South-West University projects, Group B (YMC(H)A).
18:00 - 19:30 Oral presentations OP-SH10 Psychology [PS] 6