Author(s): GUILHEM, G., POIRIER, C., AMEN, X., HEGYI, A., MACCHI, R., GIROUX, C., LACOURPAILLE, L., Institution: FRENCH INSTITUTE OF SPORT (INSEP), Country: FRANCE, Abstract-ID: 1763

INTRODUCTION:
Hamstring muscles play a crucial role in lower limb movement with potential impact on performance, e. g. sprint running [1,2]. The distribution of electromyographic (EMG) activity within hamstrings is highly variable across individuals, influences motor performance and is affected by previous injury [3,4]. Therefore, having an exhaustive understanding of the distribution of muscle activity within hamstring muscles may be particularly useful to design individualized training programs. The aim of the present systematic review was to evaluate hamstring EMG activity during strengthening exercises.
METHODS:
Databases used were PubMed, Cochrane Library, and Web of Science with publication date before First January 2023. The references list from the studies included were checked. The search (PICO) strategy selected studies including healthy adults without lower extremity injury, reporting biceps femoris long heads (BFlh) and semitendinosus (ST) activation during hamstring strength exercises. No comparison was considered due to specific cross-sectional study designs. The root mean square (RMS) expressed as a percentage of maximal voluntary isometric contraction and activation ratio (BFlh/ST) were primary outcomes. Nine inclusion criteria and six exclusion criteria were checked by two distinct investigators. Hierarchical ascending classification was applied to cluster strengthening exercises according to BFlh and ST activation.
RESULTS:
The search strategy found 302 studies after checking for duplicates. After inclusion screening, 58 studies analysing 23 different exercises were considered. Muscle activations were highly variable across studies, ranging from 5 to 145% for BFlh and 3 to 220% for ST. Hierarchical ascending classification provided 3 different clusters. Cluster 1 exercises included exercises eliciting low activation levels (<40% MVC) preferentially oriented towards BLfh (leg raise, sit-up, leg press, lunge, squat, good morning, kettlebell swing). Cluster 2 included exercises eliciting high activation levels (>80% MVC) preferentially oriented towards BFlh (sprint, knee curl and leg curl). Custer 3 included exercises with moderate activation levels (40 to 60% MVC) oriented towards ST (sidewise jump, bridge, hip thrust, Sorenssen, Nordic hamstring, unilateral bridge, drop jump, forward jump, hip hinge, cable pulley, deadlift, glider and hip extension).
CONCLUSION:
A substantial amount of literature describes medial and lateral hamstring activation across various types of exercises. Significant variability in muscle activation is reported, likely due to differences in movement amplitude, exercise intensity (loading) and posture or execution variations. Independently from these factors, the present systematic review demonstrates that exercise modality can be used to modulate muscle activation in specific muscle heads. These findings can be used by coaches and practitioners to target BFlh or ST for athletic, prevention or rehabilitation purposes.