The external validity of a novel contract-relax stretching technique on knee flexor range of motion

Compromised joint range of motion (ROM) can negatively affect the capacity to perform activities of daily living in clinical populations. Recently, similar improvements in dorsiflexion ROM were reported following dynamometry-based contract-relax (CR) stretching and modified CR stretching technique (stretch-return-contract [SRC]) where the contraction phase was performed "off stretch." As neither the impact of SRC on other muscle groups nor the ecological validity of SRC performed in an applied environment has been tested, the acute effects of both techniques in dynamometry- (CR_dyna and SRC_dyna ) and field-based (CR_field and SRC_field ) environments were compared with the hamstring muscle group.

Seventeen participants performed each of the four stretching conditions on separate days in a randomized order. Before and after the stretches, knee extension ROM and passive knee flexor moment were recorded on an isokinetic dynamometer.

Significant (P < .01) increases in knee extension ROM (4.6-5.2°) and elastic potential energy storage (12.0%-23.6%) and decreases in the slope of the passive moment-angle relation (8.9%-12.2%) occurred in all conditions. Significant increases in peak passive joint moment were observed after field- (14.3%-14.8%) but not dynamometry-based (4.6%-6.6%) stretches. No difference (P > .05) in any measure was found between conditions.

These data confirm the acute efficacy of the SRC technique in the hamstring muscle group and demonstrate its ecological validity in an applied environment in healthy participants. As the field-based SRC technique was performed without partner assistance, when compared with classical PNF it represents an equally effective and practical stretching paradigm to support athletic and clinical exercise prescription.