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

The main purpose of this study was to explore the cause-and-effect relation of maximal muscle strength (MSmax) on the optimum drop height (DHopt) 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 MSmax) 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 DHopt was determined based on the maximal value power output across applied ranges of drop heights. The tested relationships between DHopt and MSmax 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 DHopt between groups were detected (p < 0.01). The present findings suggest that drop height should be adjusted based on a subject's neuromuscular capacity to produce MSmax. Hence, from the perspective of strength and conditioning practitioners, MSmax should be considered as an important factor that could affect the DHopt, and therefore should be used for its adjustment in terms of optimizing athlete's testing, training, or rehabilitation intervention.

Pre-activity modulation of lower extremity muscles within different types and heights of deep jump.

The purpose of this study was to determine modulation of pre- activity related to different types and heights of deep jump. Sixteen male soccer players without experience in deep jumps training (the national competition; 15.0 ± 0.5yrs; weight 61.9 ± 6.1kg; height 1.77 ± 0.07m), who participated in the study, performed three types of deep jump (bounce landing, counter landing, and bounce drop jump) from three different heights (40cm, 60cm, and 80cm). Surface EMG device (1000Hz) was used to estimate muscle activity (maximal amplitude of EMG - AmaxEMG; integral EMG signal - iEMG) of five muscles (mm.gastrocnemii, m.soleus, m.tibialis anterior, m.vastus lateralis) within 150ms before touchdown. All the muscles, except m. gastrocnemius medialis, showed systematic increase in pre-activity when platform height was raised. For most of the lower extremity muscles, the most significant differences were between values of pre-activity obtained for 40 cm and 80 cm platforms. While the amount of muscle pre-activity in deep jumps from the heights above and beneath the optimal one did not differ significantly from that generated in deep jumps from the optimal drop height of 60 cm, the patterns of muscle pre-activity obtained for the heights above the optimal one did differ from those obtained for the optimal drop height. That suggests that deep jumps from the heights above the optimal one do not seem to be an adequate exercise for adjusting muscle activity for the impact. Muscle pre-activity in bounce drop jumps differed significantly from that in counter landing and bounce landing respectively, which should indicate that a higher amount of pre-activity generated during bounce drop jumps was used for performing take-offs. As this study included the subjects who were not familiar with deep jumps training, the prospective studies should reveal the results of athletes with previous experience. Key pointsHeight factor proved to be more relevant for the change in pre-activation level compared to the drop jump type factor.There is evident qualitative difference in pattern of pre-activation from lower and higher drop heights, compared to pattern of pre-activation obtained from optimal drop height.Drop jumps from the heights above the optimal one are not adequate for nicely preparing muscle activity for the impact.

Symmetry of discrete and oscillatory elbow movements: does it depend on torque that the agonist and antagonist muscle can exert?

The hypothesis that strength of active muscles affects the symmetry of the velocity profiles of voluntary movements was tested. In particular, it was assumed that the duration of acceleration and deceleration phases reflects the ability of the antagonistic muscles to exert torque in such a way that stronger muscle requires less time for action. Twelve subjects performed consecutive 50 flexions and extensions in blocks of either discrete or oscillatory movements. They were tested under high and moderate speed conditions, as well as within different ranges of elbow joint angles. The symmetry ratio (SR; acceleration time divided by deceleration time) was calculated in order to assess movement symmetry. The results demonstrated SR > 1 under most of the discrete and, particularly, oscillatory movement conditions. A velocity-associated increase in SR was recorded, while different ranges of elbow movements, assumed to provide different torques of the agonist and antagonist muscles, also provided different SR. The findings were generally in line with the predicted effects of movement conditions on muscle strength, particularly those related to elbow angle and elbow angular velocity. Deviations from the ideal movement symmetricity have usually been interpreted as either weakness of various motor control models and hypotheses, or as a sub-optimal control of movements in certain subject populations; the present study suggests an alternative interpretation based upon the ability of active muscles to exert torque