MRI-Based Regional Muscle Use during Hamstring Strengthening Exercises in Elite Soccer Players

The present study examined site-specific hamstring muscles use with functional magnetic resonance imaging (MRI) in elite soccer players during strength training. Thirty-six players were randomized into four groups, each performing either Nordic hamstring, flywheel legcurl, Russian belt or the hip-extension conic-pulley exercise. The transverse relaxation time (T-2) shift from pre-to post-MRI were calculated for the biceps femoris long (BFI) and short (BFs) heads, semitendinosus (ST) and semimembranosus (SM) muscles at proximal, middle and distal areas of the muscle length. T-2 values increased substantially after flywheel leg-curl in all regions of the BFI (from 9 +/- 8 to 16 +/- 8%), BFs (41 +/- 6-71 +/- 11%), and ST (60 +/- 1-69 +/- 7%). Nordic hamstring induced a substantial T2 increase in all regions of the BFs (13 +/- 8-16 +/- 5%) and ST (15 +/- 7-17 +/- 5%). T-2 values after the Russian belt deadlift substantially increased in all regions of the BFI (6 +/- 4-7 +/- 5%), ST (8 +/- 3-11 +/- 2%), SM (6 +/- 4-10 +/- 4%), and proximal and distal regions of BFs (6 +/- 6-8 +/- 5%). T-2 values substantially increased after hip-extension conic-pulley only in proximal and middle regions of BFI (11 +/- 5-7 +/- 5%) and ST (7 +/- 3-12 +/- 4%). The relevance of such MRI-based inter-and intra-muscle use in designing more effective resistance training for improving hamstring function and preventing hamstring injuries in elite soccer players should be explored with more mechanistic studies.