Differences In Lower-extremity Muscle Activation Patterns During Anticipated Or Unanticipated Single-leg Drop Jump Tasks

Abstract

PURPOSE: To examine the muscle activation patterns of the lower-extremity during an anticipated or unanticipated single-leg drop jump task. METHODS: Surface electromyography (EMG, 1,500 Hz) was collected from 17 healthy young male subjects (173 cm; 72 kg), including gluteus medius (GM), rectus femoris (RF), vastus medialis (VM), semitendinosus (ST), biceps femoris (BF), tibialis anterior (TA), and medial gastrocnemius (MG) on the dominant leg. Subjects were asked to drop down from a wooden box with a height of 40-cm with their dominant leg (landing), then immediately jump as high as possible (jumping). For the anticipated condition, subjects were informed of the drop jump task prior to the initial drop. For the unanticipated condition, the specific task was visually shown on the light-emitting diode screen (upwards or downwards arrow for jumping or landing, respectively), which triggered by the infrared sensor when a subject’s foot was sensed prior to initial contact (average time from sensor to initial contact: 48-ms). The data during unanticipated jumping were selectively compared to those during anticipated jumping. Time of muscle onset (time to reach 8% of peak amplitude) and time to peak amplitude were identified during the pre-contact phase (before initial contact: BIC) and the post-contact phase (after initial contact: AIC), and then analysed through t-tests (p < 0.05) and Cohen’s d effect size (d). RESULTS: Time of muscle onset of the BF (t = -2.21, p = 0.03) and TA (t = -2.76, p = 0.01) were different. Specifically, onset of the BF (116-ms BIC, d = 0.45) and TA (174-ms BIC, d = 0.56) was faster in the anticipated than the unanticipated condition (BF: 54-ms BIC; TA: 118-ms BIC). Time to peak amplitude of the GM (t = -2.51, p = 0.01), VM (t = -2.33, p = 0.02), ST (t = -2.01, p = 0.05), and BF (t = -2.69, p = 0.01) were different. Specifically, time to peak of the GM (350-ms AIC, d = 0.52), VM (365-ms AIC, d = 0.47), ST (374-ms AIC, d = 0.41), and BF (454-ms AIC, d = 0.54) was faster in the anticipated than unanticipated (GM: 439-ms AIC; VM: 451-ms AIC; ST: 472-ms AIC; BF: 646-ms AIC). CONCLUSIONS: When the task was unanticipated (between either landing or jumping after a drop landing from a 40-cm), the onset of the BF and TA were delayed during pre-contact while the GM, VM, ST, and BF were delayed reaching the peak amplitude during the post-contact phase.