Hamstring force and stretch during progressively increasing running speeds and the eccentric phase of resistance training exercises commonly used for injury prevention and rehabilitation.

The bilateral Romanian deadlift (RDL) produced significantly greater peak force in the biceps femoris long head (BFlh) and semimembranosus (SM) than any other resistance training or gait task.

• BFlh peak force during RDL: 1.6 BW (95% CI 1.5 to 1.7)
• SM peak force during RDL: 1.9 BW (95% CI 1.8 to 2.1)
• Both comparisons were significant at p<0.001 versus all other resistance training and gait tasks
• Twenty participants (10 male, 10 female) performed two sets of six repetitions of each exercise at RPE ≥8/10

Four resistance training exercises generated peak BFlh forces that were not significantly different from maximum speed sprinting.

• Maximum speed sprinting BFlh peak force: 1.0 BW (95% CI 0.9 to 1.1)
• Unilateral hamstring bridge: 1.1 BW (95% CI 0.9 to 1.2), p≥0.433
• Unilateral eccentric hip extension, unilateral eccentric slider, and Nordic hamstring exercise (NHE) each produced 0.9 BW (95% CI 0.8 to 1.0), all p≥0.433
• These comparisons were non-significant (p≥0.433) relative to sprinting

The RDL and unilateral hamstring bridge produced significantly greater peak musculotendinous unit stretch than any other task for BFlh, SM, and ST.

• Both RDL and unilateral hamstring bridge were significantly greater than all other tasks for BFlh, SM, and ST (p<0.001)
• Musculotendinous unit stretch was estimated using musculoskeletal modelling with MRI, EMG, and 3D motion capture data
• This finding applied across all three hamstring muscles examined

The Nordic hamstring exercise (NHE) and unilateral eccentric slider produced significantly lower hamstring stretch than any other task.

• NHE and unilateral eccentric slider had significantly lower stretch than all other tasks (p<0.001)
• Exception: the hip thrust for the ST was not significantly different from NHE and unilateral eccentric slider (p≥0.143)
• This low-stretch finding applied to BFlh, SM, and ST

The hip thrust produced hamstring force demands less than walking for at least some muscles.

• The paper explicitly states that force and stretch demands ranged from 'less than walking (eg, hip thrust) to more than sprinting (eg, RDL)'
• The hip thrust was also not significantly different from the NHE and unilateral eccentric slider for ST stretch (p≥0.143)
• Participants performed two sets of six repetitions of each exercise at RPE ≥8/10

Differences in hamstring force and stretch between exercises and running tasks depended on the specific hamstring muscle investigated.

• Three muscles were analyzed separately: biceps femoris long head (BFlh), semimembranosus (SM), and semitendinosus (ST)
• Musculoskeletal modelling incorporated individual MRI data, electromyography, and three-dimensional motion capture
• The authors specifically note that exercise selection strategies should account for which hamstring muscle is being targeted

The study used a cross-sectional design with 20 active participants performing both gait tasks at four speeds and seven resistance training exercises.

• Ten male and 10 female active participants were recruited
• Gait tasks included walk, jog, run, and sprint at 50%, 75%, and 100% of maximum effort on a treadmill
• Seven resistance training exercises were performed for two sets of six repetitions each at RPE ≥8/10
• Data from MRI, EMG, and 3D motion capture were combined with musculoskeletal modelling to estimate muscle forces and musculotendinous unit stretch
• Two trials were completed for each gait speed condition