Muscle stretch amplitude and load associated with vertical jump performance, muscle elastic/contractile properties, and myoelectrical activity
Morales, Jacobo Osvaldo. University of Maryland, College Park, ProQuest Dissertations Publishing, 1990. 9030963.
Eleven male subjects participated in a study to examine the influence of skeletal muscle stretch amplitude and load on vertical jump performance, muscle's elastic/contractile properties, and myoelectrical activity. Average integrated electromyograms (IEMG), knee joint angular displacement, vertical ground reaction force, and vertical jump height were measured while subjects executed maximal voluntary static jumps (SJ), counter-movement jumps (CMJ), and drop jumps (DJ) on a Kistler force platform. Subjects performed DJs from heights of 40 (DJ40) and 55 cm (DJ55). All jumps were performed with a small and large knee angle amplitude. Average IEMG activity was recorded from the vastus lateralis, gluteus maximus, and gastrocnemius muscles of the right leg. Knee angular displacement was recorded using an Penny-Giles electroganiometer fixed to the lateral side of the left knee joint. Mechanical eccentric and concentric parameters (e.g., force, velocity) derived from CMJs and DJs were compared to jumps without an active stretch (SJs). Information dealing with the behavior of the muscle's elastic/contractile properties during the various jump tests was obtained by examining the average IEMG/Force (I/F) ratios corresponding to the concentric contraction phases.
For vertical jumps involving active stretch (CMJ, DJ40, and DJ55), the jump height and average concentric force were influenced more by stretch amplitude (knee angle) than by stretch load (drop heights). The greater the stretch amplitude, the higher the jump height (p $<$ 0.01) but the smaller the resulting force (p $<$ 0.01).</p>
For average concentric velocity and power, the greater the stretch load, the greater the resulting velocity and power (CMJ vs DJs, p $<$ 0.05); the greater the stretch amplitude, the greater the velocity (DJs only, p $<$ 0.05) but the smaller the resulting power (CMJ and DJs, p $<$ 0.01).</p>
Only for the gastrocnemius, the greater the stretch load, the lower the resulting I/F ratio (CMJ vs DJ55, p $<$ 0.05) regardless of stretch amplitude. It was concluded that the gastrocnemius shows a greater utilization of elastic/contractile potentiation compared to the vastus and gluteus muscles.
Regardless of stretch amplitude, load, and muscle, the average IEMG activity corresponding to the concentric contraction was greater than that of the eccentric contraction (p $<$ 0.05). It was concluded that long-latency reflexes are involved in active stretch jumping in which the eccentric contraction is at least 150 milliseconds long. This involvement was not dependent on stretch amplitude and load.