Changes In Anatomical Cross-sectional Area Following 6 Weeks Of Eccentric Hamstring Training

Eccentric (ECC) strength training induces muscle architectural and morphological adaptations. The Nordic hamstring exercise (NHE) is the most evidence-based intervention for modifying injury risk factors, such as biceps femoris long head (BFlh) fascicle length. Most studies have assessed architectural changes of BFlh, but have not investigated anatomical cross-sectional area (ACSA) of the hamstring group. PURPOSE: To investigate the effects of a 6 week volume-, intensity-, and ECC time-matched Romanian deadlift (RDL) and NHE training intervention on changes in ACSA. METHODS: Participants were randomly assigned into either the RDL or NHE training group. Three transverse view images were collected in the dominant limb using extended field-of-view imaging at the midpoint of the thigh before and after the training intervention. Cross-sectional areas of BFlh, semitendinosus (ST), and semimembranosus (SM) muscles were measured in each image and then averaged for each participant for subsequent analysis. A linear mixed effects model was used to determine differences in ACSA between muscle, group, and time (main effects) with subject as a random effect. Summary data are presented as mean (standard deviation) and model outputs are presented as estimate [95% confidence interval]. RESULTS: A total of 15 participants were included across the RDL (n = 8, 20.5 (1.1) years, 172 (9.1) cm, 69.6 (4.8) kg), males = 5) and NHE groups (n = 7, 21.1 (1.2) years, 170.3 (10.9) cm, 70.1 (11.8) kg, males = 4). No significant interactions were observed (p > 0.50 for all). No significant differences were noted following training (baseline-post difference: 0.16 [-0.32, 0.63] cm2, p = 0.51) or between groups (RDL: (9.69 [8.66, 10.71] cm2, NHE: 8.31 [7.22, 9.41] cm2, p = 0.07). There were significant differences between each of the three hamstring muscles (BFlh: 11.2 [10.4, 12.0] cm2 > SM: 9.2 [8.4, 10.0] > ST: 6.7 [5.9, 7.5] cm2, p < 0.01 for all pairwise comparisons). CONCLUSION: ECC training did not alter ACSA for any of the hamstring muscles following 6 weeks of training. The training intervention was likely not long enough to induce hypertrophy. A larger sample size is needed to determine if the borderline significance between groups is meaningful. Further research should investigate the relationship between ACSA and architectural features.