Task-specific initial impact phase adjustments in lateral jumps and lateral landings

Abstract

Load-dependant adjustments in lateral jumps are thought to rely on foot placement and on upper leg's kinematic and neuromuscular adaptations. The aim of this study was to elucidate task-specific adjustments during the initial impact phase under varying stretch-loads by the comparison of lateral jumps and lateral landings. Ten subjects performed lateral jumps and landings from four distances. Electromyographic (EMG) data of five lower extremity muscles were measured, whilst lower extremity kinematics and kinetics were analysed by 3D motion analysis. Lateral jumps were characterized by increased impact forces, higher lower extremity joint moments with exception of the initial knee abduction moment, greater sagittal knee and hip joint displacements, and a further exorotated foot placement. In lateral landings frontal ankle and hip joint displacements were greater. Thigh muscle and m. tibialis anterior (TA) pre-activity as well as initial post-impact EMG were higher in lateral jumps than in lateral landings, whilst during the reflex-induced phase thigh and shank muscle EMG, except for TA, were enhanced in lateral jumps. From these findings it can be concluded that task specificity in lateral jumps in contrast to lateral landings impedes a stretch-load adequate modulation of initial impact forces which particularly affects ankle joint loading. Foot placement seems to play a decisive role for limiting lateral ankle and medial knee joint loading. Therefore, in sports containing high-impact frontal plane movements a special emphasis in training routines should be paid to foot placement strategy in those movements. Such training interventions might contribute to injury prevention in lateral movements.

Pelvic floor muscle reflex activity during coughing – an exploratory and reliability study

“…It focused on the reliability of 6 previously defined EMG variables of pre-activity and reflexivity [11,18,19]. The study was conducted in accordance with the Declaration of Helsinki, and all participants gave written informed consent.…”

Pelvic floor muscle electromyography during different running speeds: an exploratory and reliability study

“…Following the study protocol of Fleischmann et al [15], who calculated EMG amplitudes of shank muscles between touchdown to 150 ms of ground contact in 30-ms time windows for lateral jumps from four different distances, the same 30-ms time intervals were calculated for all three running speeds in the present study.…”

“…Therefore, reflex phase amplitudes were calculated between 30 and 60 ms (short latency response), 60-90 ms (mid latency response), 90-120 ms (long latency response) and 120-150 ms (long latency succeeding response). Additionally, pre-activity was computed during the interval between -30 ms and T0 [10,15].…”

“…100 % of EMG equals the average of the two peak amplitude values during the two 5-s sessions of MVC. Third, EMG variables were calculated as RMS values within each 30-ms interval [10,15,16], averaged over 10 steps and normalized to peak MVC (%EMG). The different activity variables are described in Table 1.…”

“…To determine PFM EMG activity during the initial phase of ground contact, the approach according to Fleischmann et al [10,15] was chosen: As basically no clear and reproducible reflex peaks could be determined visually on the rectified EMG of consecutive steps, mean amplitudes for fixed 30-ms intervals covering the phase in which reflex activity is expected to occur were calculated. Therefore, reflex phase amplitudes were calculated between 30 and 60 ms (short latency response), 60-90 ms (mid latency response), 90-120 ms (long latency response) and 120-150 ms (long latency succeeding response).…”