Acute effects of varying densities of foam roller on hamstring flexibility and eccentric strength

Foam rolling is a popular form of self-administered soft tissue therapy, commonly used in sporting environments. There are several variations in foam roller types including differences in density. No studies have examined the effects of different density type rollers on performance. This study compares the effects of varying foam roller density on hamstring flexibility and eccentric hamstring strength in active men. A total of 28 healthy male participants (height 176.7 ± 5.9 cm; body mass 75.8 ± 9.6 kg; age 21.6 ± 4.0 years) were randomly allocated to receive a low density, medium density or high density foam roller or allocated to a control group. Outcome measures included hamstring flexibility through active knee extension (°) and eccentric hamstring strength pre and immediately-post foam roller application. Significant foam roller x time interactions were found for hamstring flexibility (P<0.05). Significant increases in active knee extension were reported post-foam roller application for all foam roller densities (P<0.05). No significant changes in strength parameters (break angle, peak and average force and torque) were found (P>0.05). No significant interactions between strength parameters, limb, type of roller or time were found (P>0.05). Foam roller use elicits immediate positive increases in hamstring flexibility through active knee extension assessment, with the lower density foam roller displaying the largest increases in hamstring flexibility. No change in strength parameters were noted with the increases in flexibility; however, this does not denote that injury risk is reduced because of this. Findings provide practitioners with insight to inform decision making for the use of different densities of foam roller in practical settings.