Papers

Motor learning of gross-motor skills under variable practice conditions

Research background and hypothesis. For both the athlete and the coach, the purpose and goal of training is the same: to enhance performance. Research aim. This study investigated the effect of differential learning on basketball free throw and volleyball strike. Research methods. In the basketball experiment, in pre-, post- and retention test design, the free throw performance was measured (number of successful shots). Aiming to investigate transfer performance, jump shots were tested. In the volleyball experiment, movement variability during the strike was further increased by the application of an elastic constraint. The second intervention and quasi-control group trained under constant practice conditions. Ball velocity and accuracy were analysed with a constant and a variable test. Research results. No significant differences were observed for either the free throw (p > 0.05) or the transfer performance (p > 0.05). However, a positive trend for the variable group was observed in the transfer situation. For the strike in volleyball, the differential learning group had a significant advantage with respect to velocity in a variable test situation (p < 0.05) whereas in the constant situation (p > 0.05) and measurements for accuracy (p > 0.05) it did not reveal similar results. Discussion and conclusions. In both experiments, the set variability leads to benefits in variable (transfer) situations. However, as a practical consequence, especially for constant situations, certain moderator variables such as training age or background in other sports or activities must be kept in mind to adjust the amount of external or intervention-induced variability. PDF Download

Constraint-led changes in internal variability in running

We investigated the effect of a one-time application of elastic constraints on movement-inherent variability during treadmill running. Eleven males ran two 35-min intervals while surface EMG was measured. In one of two 35-min intervals, after 10 min of running without tubes, elastic tubes (between hip and heels) were attached, followed by another 5 min of running without tubes. To assess variability, stride-to-stride iEMG variability was calculated. Significant increases in variability (36 % to 74 %) were observed during tube running, whereas running without tubes after the tube running block showed no significant differences. Results show that elastic tubes affect variability on a muscular level despite the constant environmental conditions and underline the nervous system’s adaptability to cope with somehow unpredictable constraints since stride duration was unaltered. Full paper and PDF-Download

The effect of an acute bout of rubber tube running constraint on kinematics and muscle activity

We examined the effect of an acute bout of treadmill running with rubber tube (RT) and without rubber tube (NT) elastic constraints on electromyographic (EMG), 3D kinematics variability, and blood lactate concentration (LA). In the RT test, the constraints were attached to the hips and ankles. The selected variables were compared between 30 min of NT running and 30 minutes of RT running in 13 healthy recreationally trained male runners who had no prior exposure to RT. Statistical analysis revealed significantly higher EMG variability (p < 0.01) and muscle activity (p < 0.05) during RT compared to NT that decreased over time approaching NT, indicating movement pattern adaptation. 3D-kinematics and their variability remained gener- ally unaltered. Changes occurred predominantly in the sagittal plane, specifically to the knee and the swing. A significant increase in LA was measured at the end of RT (p < 0.05). These findings suggest that RT running influences muscle recruitment and variability, but has only a minor influence on kinematics. Changes in LA were significant, although relatively small. The observed adaptations in EMG and kinematics suggest that the RTs provide a possibility to create within movement variability in various sports, and thus, variable training conditions may foster strategies to increase the ability to flexibly adapt to different and new situations. Full paper and PDF-Download

The influence of external perturbations on running kinematics and muscle activity before and after accommodation

In the current study, the running pattern of the lower extremity was examined while being perturbed through tubes attached between the ankles and the lower back to analyze influences on the running pattern variability before and after a varied running intervention. 3D-kinematics, joint coupling and electromyography (EMG), as well as their variability, were analyzed in ten healthy male participants during treadmill running (10.5 km·h-1). Pre- and post-tests each consisted of 2 x 30 min treadmill running (one with and one without tubes). The results showed major acute effects on EMG and kinematics, as well as joint coordination variability, due to the constraints (p < 0.05). After the intervention, a process of normalization of most kinematic and EMG parameters occurred; however, EMG variability, kinematic variability and joint coordination variability were reduced during tube running below normal running level (p < 0.05). The findings further indicate rapid kinematic adaptations while muscle activity appears to require longer practice to adapt. The constraint serves to acutely increase variability, but may lead to reduced variability when applied for a longer period of time. Full paper and PDF-Download

Physiological responses in ski tourers walking with support of elastic cords

Aim. It was our objective to assess the effect of the supportive use of elastic cords (due to their influences on reactive phenomena) on the energy cost of a 30 min and 1.5 hrs-ski touring trial, respectively. Methods. Seventeen trained male and female ski tourers performed two treadmill walk- ing trials of 30 min each at an individually a priori defined speed (range 3-5 km∙h-1) at 24% grade. Additionally, 3 of the participating males also did two 1.5 hr-walks. The cords were attached from the front of the hip to the toe piece of the binding, with the length be- ing individually adjusted to achieve similar support by the cords. To estimate differences in physiological response and individual exertion, measurements included breath-to- breath spiro-ergometry, lactate, heart rate and rate of perceived exertion. Results. There were no significant changes in group means of the physiological parameters for the 30-min intervals; however, ratings of perceived exertion were significantly lower during cord walking. For the longer measurements, data hint towards a supportive effect of the cords as physiological data are below normal walking data and ratings were again lower. Conclusion. While 30 min walking with elastic cords does not demonstrate a difference in measured physiological response, perceived exertion is affected. This perceived difference may only be noticeable when walking for a longer period of time, which as indicated by long-term experimental data is indicative of a ski tour. This may also hint towards a potential utilization of the supportive forces produced by the cords. Full paper

The effect of external perturbations on variability in joint coupling and single joint variability

This paper explores the effect of goal-oriented external perturbations created by elastic tubes attached to the hip and ankles on lower limb joint variability and hip–knee and knee–ankle coordination variability during running. Kinematics of ten healthy male runners were analysed prior to and following a 7-week tube running intervention while running with and one without this constraint. The training intervention was based on variable training aspects to increase within-movement variability and adaptability of the running pattern. To analyse the effects of the tubes on the running pattern, the phase plot vector length deviation (i.e., the standard deviation of the phase plot vector length) for the within-joint variability and the continuous relative phase variability for the joint coupling variability were calculated. Results revealed acute increases of variability in both parameters. However, after the intervention, variability of the tube running situation returned to normal for all couplings and joints except the knee. No transfer effects to normal running were observed. This suggests very rapid adaptations to such perturbations. In the long-term, it may ask for more or different variations. Full paper

Blood lactate response, oxygen consumption and muscle activity during treadmill running with a special rubber tubing constraint

Summary.—The induction of self-organization during running with a special harness may lead to reduced energy requirements. This experiment was designed to investigate the effect of practicing with a rubber tubing constraint attached between the heel and the hip for 7 weeks (18 treadmill running sessions) on oxygen consumption, caloric unit cost, blood lactate concentration, and muscle activity. 18 male recreational runners (M age = 26.3 yr.) were assigned to either an intervention or a control group. The intervention group trained with the constraint, the control group trained without it. Test 1 was conducted before the intervention, Test 2 after the intervention, and Test 3 was 7 weeks after Test 2 (no training between Tests 2 and 3). At Test 1, lactate and muscle activity were significantly increased during constrained running. For lactate, a significant decrease was found in the intervention group for running with the constraint; at Test 3, lactate returned to Test 1 level. No notable changes occurred in the physiological parameters. Furthermore, there was no observed transfer effect on normal running. Full paper (sobald online verfügbar)

Short and long term adaptation of variability during walking using unstable (Mbt) shoes

Background: The purpose of the study was to compare the variability of biomechanical variables during treadmill walking using unstable shoes (Masai Barefoot Technology, MBT, Roggwil, Switzerland) and conventional shoes, before and after a 10 week (wk) training period. Methods: Cycle characteristics, plantar pressure distribution, whole body 3D kinematics, and electromyographic signals of selected leg muscles during ground contact were recorded on 12 Sport Science students while walking on a treadmill with both conventional and unstable shoes before and after a 10 wk training intervention. The intervention consisted of more than 4 h use of unstable shoes during daily activity. The standard deviation of 15 consecutive cycles in each analyzed variable was taken as the measure for variability. Findings: The main pattern was marked by a 35% (SD 10%) higher variability with the unstable shoes at pretest when compared with the conventional shoes, but decreased 30% (SD 12%) (both Pb0.05) during the training intervention to almost equal variability in between the two shoe situations. This was especially true with regard to variables representing within gait characteristics (peak foot force, joint angles, etc.), whereas in variables describing the overall gait cycle (e.g. cycle rate, impulse of total force, etc.) no difference between MBT and conventional shoes at pre and post tests were found. Interpretation: The current study supports the idea that the unstable shoe serves as a motor constraint applicable during everyday activity, provoking increased variability during walking. In addition, a decrease in movement variability on the MBT shoes during the training intervention to the level of conventional shoes was observed. Full paper

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