Phase- and task-specific modulation of soleus H-reflexes during drop-jumps and landings.
H-reflexes in the soleus muscle were previously shown to be decreased in drop-jumps at the instant of the short latency response (SLR) of the stretch reflex when falling height was increased. The aim of the present study was to elucidate task-specific modulation of H-reflexes during drop-jumps in more detail. Therefore, soleus H-reflex excitability was compared in drop-jumps from three different falling heights (30, 50, 75 cm) and between drop-jumps and landings. In landings, there is no need for high tendomuscular stiffness like in drop-jumps. Therefore, we assumed reduced spinal excitability of soleus Ia afferents which should be reflected as reduced H-reflexes. H-reflex recruitment curves were recorded in 23 subjects (24 +/- 2 years) at the instant of the SLR during drop-jumps (30 cm-LH, 50 cm-MH, 75 cm-EH) and landings (30 cm falling height). Furthermore, recruitment curves were recorded at ground contact (GND) as a reference to SLR. At SLR, H/M ratios were higher during drop-jumps (LH: 0.49 +/- 0.18) than during landings (0.33 +/- 0.18, P < 0.001). H/M ratios did not differ at GND (LH: 0.46 +/- 0.15; landings: 0.46 +/- 0.14). H/M ratios were progressively decreased at the SLR from LH, to MH, to EH (MH: 0.44 +/- 0.17; EH: 0.40 +/- 0.16, P < 0.001). Again, there were no differences at GND (MH: 0.46 +/- 0.15; EH: 0.44 +/- 0.16). The present study provides further evidence of phase-specific (GND vs. SLR) and task-specific modulation of SOL Ia afferent input. These modulations were thought to be initiated prior to touch down.
Department of Sport Science, University of Freiburg, Schwarzwaldstr. 175, 79117, Freiburg, Germany. christian.leukel@sport.uni-freiburg.de
Christian
C
Leukel
Albert
A
Gollhofer
Martin
M
Keller
Wolfgang
W
Taube
D000222:Adaptation, Physiological / Q000502:physiology*; D000328:Adult; D000344:Afferent Pathways / Q000502:physiology; D054874:Athletic Performance / Q000502:physiology; D001696:Biomechanical Phenomena; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000502:physiology*; D006801:Humans; D007866:Leg / Q000294:innervation / Q000502:physiology*; D008297:Male; D009048:Motor Skills / Q000502:physiology; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009470:Muscle Spindles / Q000502:physiology*; D018482:Muscle, Skeletal / Q000294:innervation / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology; D016474:Weight-Bearing / Q000502:physiology