Hoffmann’s reflex (the H-reflex) is an electrically-induced reflex that is analogous to the mechanically-induced stretch reflex controlled by the spinal cord. The most common measurements performed concerns the electrical response of the soleus muscle to electrical stimulation in the tibial nerve. The response is induced by a discharge occurring in a motoneuron. The latency time of the H-reflex for the soleus muscle amounts to 30–40 ms. An increase in the strength of the stimulus induces a direct response from the muscle, i.e. the M-wave. The latency time of the M-wave amounts to 4–5 ms. A sport training may affect the parameters of the H-reflex. The Hmax/Mmax ratio is the highest among persons engaged in endurance sports and the lowest among those practising speed and strength sports. A decreased amplitude of the H-reflex characterises the level of the central fatigue, while a decrease in the M-wave amplitude is attributed to the peripheral fatigue. Usually, a decrease in Hmax/Mmax ratio is observed post-exercise. Different times of recovery were reported in the literature. No clear quantitative laws have yet been established that govern the course of the reflex as a result of fatigue. The H-reflex still remains within the scope of the interests of kinesiology as a valuable source of information about the reflex functions in the human motor system.
Key words: H-reflex, M-wave, central fatigue, peripheral fatigue, electrical stimulation
Purpose. Back pain is a frequent symptom in the obese. The purpose of the study was to compare the effects of two training programs on the reduction of back pain among obese women. Methods. The study included 30 obese women who reported back pain within 3 months preceding enrollment. The subjects were randomly allocated to endurance or endurance/resistance physical exercise. The intensity of the exercise was adjusted to 50–80% of Hrmax. Back pain intensity, muscle strength of knee flexors and extensors, body balance and body composition were measured before and after training. Results. Both the endurance and endurance/resistance training exerted positive effect on back pain (p < 0.05). Similarly, in both training groups the significant increase in the strength of knee flexors and marked reduction of body fatness (p < 0.001 for all) was documented. However, the interventions’ efficacies in selected groups did not differ. Conclusions. Both endurance and combined endurance/resistance training exert positive effect in decreasing back pain and improving functional fitness of obese women. Therefore, both forms of training may be recommended for individuals dealing with the abovementioned problems.
Key words: aerobic exercise, back pain, obesity
Purpose. In Front-Crawl swimming stroke, the interaction between two of its components, i.e. arm stroke and breathing, affects the performance of the motor skill as a whole and therefore can be considered a critical aspect of the skill. The purpose of our study was to investigate if a verbal instruction emphasizing this interaction could lead to learning gains when provided along with video demonstrations. Methods. Participants (children) were randomly assigned to three experimental groups according to the type of verbal instruction provided. Component and Interaction groups received their specific instructions along with video demonstrations of a model execution of the Front-Crawl. The Control group watched the same video, but received no further instruction concerning the movement pattern. In the Acquisition phase (AQ) all groups performed 160 trials (organized in 4 sessions) of the task that consisted in swimming 8 meters the Front-Crawl at a comfortable velocity. To assess learning gains, a retention test (RT) and a transfer test (TR) were carried out one week after the end of the AQ. Results. Regarding RT and TR, the one-way ANOVA on the movement pattern score showed a significant difference between groups, with post-hoc tests revealing that the Interaction group achieved higher score than the Control group. Conclusions. The results reveal that enhancing aspects of a video demonstration with verbal instruction improves learning gains of the Front-Crawl in children. Additionally, the results suggest that providing verbal instructions about the interaction between stroke and breathing might promote learning gains, compared to providing instructions about the stroke component individually.
Purpose. The appropriate percentage of body fat is essential for women’s health and biological condition. both accumulation of fat and distribution pattern of adipose tissue are connected with health risk, which justifies the investigation and permanent monitoring of their diversity in different sub-populations. The aim of the study was to evaluate the percentage of body fat and its distribution in female students representing different physical activity levels. Methods. Fat proportion was estimated with use of classic anthropometric method and bioelectrical impedance analysis (BIA). The distribution of subcutaneous fat was calculated including waist and hip circumferences, and extremities and trunk skinfolds. The participants’ level of physical activity was determined according to the IPAQ questionnaire. Results. Analysis showed that female students with medium level of physical activity had 26.5 ± 5.1% of total body fat estimated by BIA, whereas in the most active females almost 3% lower total body fat values were common. The bioelectrical impedance analysis indicated about 8% higher body fat content than classic anthropometry. Examined skinfolds revealed a tendency to decrease with increasing physical activity. The distribution pattern of subcutaneous fat varied according to level of activity. Conclusions. The study showed that estimation of fat content in young women differed depending on the applied method and the level of physical activity. We emphasize the need to select adequate reference data for measurement methods and consider the level of physical activity during fat percentage assessment. Another conclusion is that the high level of physical activity is connected with masculinization of subcutaneous fat pattern, both in extremities/trunk fat proportion and waist/hip proportion.
Purpose. This study estimates the contribution of reaction time and movement velocity to the reactive agility time while covering varied distances. Methods. A total of 95 athletes of karate, hockeyball and soccer participated in a simple reaction, two choice reaction, step initiation and reactive agility test. Results. Agility time was significantly better in karate-kumite than karate-kata practitioners when covering a distance of 0.8 m (8.2%, p = 0.045), better in hockeyball players than goalies when covering a distance of 1.6 m (10.9%, p = 0.028) and better in soccer players than goalies when covering a distance of 3.2 m (14.2%, p = 0.009). Movement velocity to agility time contributed to a lesser degree in the case of karate-kata competitors, hockeyball and soccer players (33.5%, 28.3%, and 19.9% respectively) than the karate-kumite competitors, hockeyball and soccer goalies (44.2%, 42.7%, and 39.4% respectively). Furthermore, both simple and two choice reaction times were highly related to the agility time when covering distances of 0.8 m, 1.6 m, and 3.2 m (r in range from 0.72 to 0.88). Movement velocity also significantly correlated with the agility time in the test with a distance of 0.8 m (r = 0.76) but not with longer movement distances of 1.6 (r = 0.61) and 3.2 m (r = 0.52). Conclusions. reaction time and movement velocity differentially contribute to the agility time in athletes of varied specializations. This reflects their specific demands on agility skills, and therefore should be addressed in agility testing in order to identify an athlete’s weakness.
Purpose. To assess the effects of an 11-week Pilates exercise program on the functional capacity of young sedentary women. Methods. Ten subjects underwent the shuttle walking test. A portable metabolic system was used during the shuttle walking test to measure the maximum heart rate and VO2 max. The heart rate recovery and the predicted maximal heart rate were also assessed. Results. The findings showed increased walking distance, maximum heart rate and heart rate recovery after completing the protocol. The peak of VO2 was not significantly different but showed a tendency to increase, being significantly correlated with the covered distance. Conclusions. The current results suggest that Pilates exercises significantly improve walking functional capacity.
Purpose. The purpose of this study was to compare the inter-joint coordination during sit-to-stand (STD) and stand-to-sit (SIT) execution between healthy people and people with low back pain. Methods. Fifteen healthy adults (age = 45.14 ± 5.18 years) and fifteen age-matched (age = 46.17 ± 8.26 years) people with chronic low back pain were selected voluntarily. They performed three repetitions of STD and SIT movement patterns in their preferred pace. Motion analysis system was used for measuring 3-dimensional (3D) angular displacement of hip, knee and ankle joints during execution of movement patterns. Decomposition indices were analysed and were compared between two groups through Hotelling T2 Multivariate Analysis of Variance (MANOVA) and follow-up Analysis of Variance (ANOVA). Results. The results showed that there is a significant difference (T2 = 18.32, F14, 5 = 8.33, p < 0.05) between the groups on decomposition indices. The ANOVA follow-up results showed that there are significant differences between two groups on decomposition indices of the whole pattern of STD (F1, 18 = 7.96, p < 0.05), whole pattern of SIT (F1, 18 = 5.37, p < 0.05), the first-half phase of STD (F1, 18 = 7.26, p < 0.05) and the first-half phase of SIT (F1, 18 = 6.33, p < 0.05). Conclusions. People with low back pain have dis-coordination in the function of different body parts, and results in pausing of one segment while the other segment moves independently. This knowledge may help in the development of rehabilitation strategies for movement in this population.
Purpose. The aim of the current study was to comparatively examine the effects of energy return, spring and conventional footwear on the kinetics and kinematics of running. Methods. Twelve male runners ran over an embedded force platform at 4.0 m · s−1 in the three footwear conditions. Lower limb kinematics were collected using an 8 camera motion capture system and tibial accelerations were obtained using an accelerometer. Differences in kinetic and kinematic parameters between footwear were examined using one-way repeated measures ANOVA. Results. The results showed that there were no significant differences in kinetic parameters between footwear. However, it was shown that that spring footwear were associated with significantly greater angles of peak eversion (−12.49°) and tibial internal rotation (13.09°) in comparison to the conventional footwear (eversion = −10.52° & tibial internal rotation = 10.84°). Conclusions. Therefore, the findings from the current investigation indicate that spring footwear may place runners at increased risk from chronic injury related to excessive ankle eversion/tibial internal rotation.
Purpose. Snowboarding requires a lateral positioning of the body. Moreover, a person must continuously control their balance and use this in order to manoeuvre on the slope applying properly pressure on the lower limb closest to the nose of the board (the leading leg). The present study is an attempt to determine the interdependencies between side preference while snowboarding and laterality when performing other tasks. The dynamic stability in the neutral standing position, as well as in the lateral positions (left or right) was also evaluated. Methods. The survey participants (100 active snowboarders) answered a set of questions concerning laterality while carrying out basic everyday tasks and while doing sports. The respondents were divided into two groups based on their preferred leading side in snowboarding. Additionally, in the case of 34 people, muscle torques values of the lower limbs were measured under static conditions and the postural stability was evaluated using AccuSway AMTI platform and Biodex Balance System platform. Results. Over 90% of the participants declared right-handedness and right-footedness. However, with regard to snowboarding, only 66% indicated their right leg as leading. No significant dependence was found between the directional stance on the board and the leading hand, dominant leg, or leading eye. The stability measurements revealed statistically significant differences between the neutral stance and the lateral positioning. Conclusions. Based on the study results, it may be assumed that the declared directional stance on the snowboard is not contingent on the person’s basic laterality, and that the lateral stance on the board significantly affects the posture control.
Purpose. The aim of this study was to examine the relationship between impulsiveness and tactical performance of U-15 youth soccer players. Methods. The sample comprised 100 U-15 youth soccer players. Impulsiveness and tactical performance were assessed using the Continuous Performance Test-II (CPT-II) and the System of Tactical Assessment in Soccer (FUT-SAT), respectively. FUT-SAT enables evaluation of ten core tactical principles of soccer game: (i) penetration; (ii) offensive coverage; (iii) depth mobility; (iv) width and length; (v) offensive unity; (vi) delay; (vii) defensive coverage; (viii) balance; (ix) concentration; and (x) defensive unity. Impulsiveness values were obtained using the Omission and Commission Error analysis. Tactical performance values were obtained through the Game Tactical Performance Index (GTPI), Offensive Tactical Performance Index (OTPI) and Defensive Tactical Performance Index (DTPI). The Kolmogorov–Smirnov test and Spearman’s Correlation one were performed (p < 0.05) through SPSS, v. 22. Results. We observed a positive correlation between impulsiveness and GTPI (rho = 0.226; p = 0.018). Conclusions. It is concluded that impulsiveness is related to tactical performance of U-15 youth soccer players.
University School of Physical Education in Wrocław
al. I. J. Paderewskiego 35
51-612 Wrocław, Poland