Duško Ilić

The effects of practice on movement distance and final position reproduction: implications for the equilibrium-point control of movements

Predictions of two views on single-joint motor control, namely programming of muscle force patterns and equilibrium-point control, were compared with the results of experiments with reproduction of movement distance and final location during fast unidirectional elbow flexions. Two groups of subjects were tested. The first group practiced movements over a fixed distance (36°), starting from seven different initial positions (distance group, DG). The second group practiced movements from the same seven initial positions to a fixed final location (location group, LG). Later, all the subjects were tested at the practiced task with their eyes closed, and then, unexpectedly for the subjects, they were tested at the other, unpracticed task. In both groups, the task to reproduce final position had lower indices of final position variability than the task to reproduce movement distance. Analysis of the linear regression lines between initial position and final position (or movement distance) also demonstrated a better (more accurate) performance during final position reproduction than during distance reproduction. The data are in a good correspondence with the predictions of the equilibrium-point hypothesis, but not with the predictions of the force-pattern control approach.

Role of agonist and antagonist muscle strength in performance of rapid movements.

Six subjects performed rapid self-terminated elbow movements under different mechanical conditions prior to, and 5 weeks after an elbow extensor strengthening programme. Despite the large difference in the strengths of elbow flexors and extensors, the pretest did not demonstrate significant differences between the movement time of flexion and extension movements performed under the same mechanical conditions. The results obtained in the posttest demonstrated a decrease in movement time (i.e. an increase in movement speed) in both elbow flexion and extension movements under some mechanical conditions. In addition, flexion movements demonstrated a relative increase in the acceleration time (acceleration time as a proportion of the movement time). It was concluded that the strength of both the agonist and antagonist muscles was important for the performance of rapid movements. Stronger agonists could increase the acceleration of the limb being moved, while stronger antagonists could facilitate the arrest of the limb movement in a shorter time, providing a longer time for acceleration.

The effects of practice on movement reproduction: Implications for models of motor control

This study investigated how consistently and accurately subjects could reproduce final movement position when performing three different movement tasks over four experimental sessions. Task 1 involved moving five different inertial loads over one movement distance. Task 2 involved performing movements over five different distances against a constant inertial load. Task 3 involved moving five distances against five inertial loads that were adjusted to keep movement time relatively constant. Subjects who had practised Task 1 demonstrated the largest decrease in variable error over experimental sessions but little change in constant error. Subjects who had practised Task 2 showed a smaller improvement in variable error and no improvement in constant error. Subjects who had practised Task 3 demonstrated a small change in variable error and an improvement in constant error. The largest reduction in variable error in the first group is consistent with the equilibrium-point hypothesis of motor control but not with force-control models. The improvement in constant error in the third group is discussed with respect to a possible role of noise in practising simple movements.

Walking at speeds close to the preferred transition speed as an approach to obesity treatment.

INTRODUCTION Increasing energy expenditure through certain exercise is an important component of effective interventions to enhance initial weight loss and prevent weight regain. OBJECTIVE The purpose of this study was to determine the effect of a 16-week weight loss exercise programme on morpho-functional changes in female adults and to examine the programme effects on two subpopulations with different levels of obesity. METHODS Fifty-six middle-aged women were divided into 2 groups according to their body mass index (BMI): 25-29.9 kg/m2--overweight (OW) and > or =30 kg/m2--obese (OB). The exercise protocol included a walking technique based on hip rotation at horizontal plane at speeds close to the preferred transition speed (PTS). At the initiation of the study and after 16 weeks of the programme, anthropometric, morphological and cardiovascular parameters of all subjects were assessed. The main effects of Group (OW and OB) and Time and the interaction effect of Group by Time were tested by time repeated measures general linear model (mixed between-within subjects ANOVA). RESULTS Mean weight loss during the programme was 10.3 kg and 20.1 kg in OW and OB, respectively. The average fat mass (FM) loss was 9.4 kg in OW and 16.9 kg in OB. The mixed ANOVA revealed a significant group by time interaction effects for waist circumference, body weight, body water, fat free mass, FM, %FM and BMI (p < 0.05). CONCLUSION The applied exercise protocol has proved as beneficial in the treatment of obesity, since it resulted in a significant weight loss and body composition changes. The reduction in body weight was achieved mainly on account of the loss of fat mass.

Optimum Drop Height for Maximizing Power Output in Drop Jump: The Effect of Maximal Muscle Strength

Abstract Matic, MS, Pazin, NR, Mrdakovic, VD, Jankovic, NN, Ilic, DB, and Stefanovic, DLJ. Optimum drop height for maximizing power output in drop jump: The effect of maximal muscle strength. J Strength Cond Res XX(X): 000–000, 2015—The main purpose of this study was to explore the cause-and-effect relation of maximal muscle strength (MS max ) on the optimum drop height (DH opt ) that maximizes power output in drop jump. In total, 30 physically active male students participated in this study, whereas the 16 subjects were selected according to their resistance strength training background (i.e., level of MS max ) and allocated into 2 equal subgroups: strong (n = 8) and weak (n = 8). The main testing session consisted of drop jumps performed from 8 different drop heights (i.e., from 0.12 to 0.82 m). The individual DH opt was determined based on the maximal value power output across applied ranges of drop heights. The tested relationships between DH opt and MS max were moderate (r = 0.39–0.50, p ⩽ 0.05). In addition, the stronger individuals, on average, showed maximal values of power output on the higher drop height compared with the weaker individuals (0.62 vs. 0.32 m). Finally, significant differences in the individual DH opt between groups were detected (p < 0.01). The present findings suggest that drop height should be adjusted based on a subjects neuromuscular capacity to produce MS max . Hence, from the perspective of strength and conditioning practitioners, MS max should be considered as an important factor that could affect the DH opt , and therefore should be used for its adjustment in terms of optimizing athletes testing, training, or rehabilitation intervention.