Effects of Combining PNF With NMES in Young Football Players

NMES is applied during each 10-second isometric hamstring contraction using an Enraf Nonius TensMed S82 stimulator delivering biphasic, symmetric rectangular pulses at 50 Hz with a 250 µs pulse width. Two 5 × 5 cm self-adhesive electrodes are placed on the hamstrings-one approximately two finger-breadths below the gluteal fold and the other over the distal third of the muscle belly. Stimulation intensity is individually titrated to each participant's maximal motor threshold-eliciting a strong, yet painless, contraction-and the exact milliamperage is recorded for each leg. Elastic straps over the pelvis and distal thigh maintain pelvic anteversion and knee extension. During each session, one researcher secures limb positioning while a second adjusts and logs NMES intensity and cues the timing of the 10 s contraction and ensuing 30 s passive stretch.

Sham NMES is delivered during each 10 s isometric hamstring contraction using an Enraf Nonius TensMed S82 stimulator with biphasic, symmetric rectangular pulses (50 Hz, 250 µs pulse width). Two 5 × 5 cm self-adhesive electrodes are placed on the hamstrings-one two finger-breadths below the gluteal fold and one over the distal third of the muscle belly. Intensity is individually set to the sensory threshold, defined as the minimal current producing a slight tingling without any visible muscle response; this milliamperage is recorded for each leg. Elastic straps over the pelvis and distal thigh maintain pelvic anteversion and full knee extension. During each session, one researcher secures limb positioning while a second adjusts and logs the NMES intensity and cues the 10 s contraction timing.

The crPNF Group engages in an isolated contract-relax proprioceptive neuromuscular facilitation (crPNF) stretching protocol. Participants are positioned in a long sitting posture with maximum knee extension until they feel a moderate-strong stretch sensation, without pain. Each stretch lasts for 30 seconds, followed by a 10-second maximal voluntary isometric contraction of the hamstrings. Participants complete three cycles of stretch and contraction. One researcher maintains the stretch position while a second researcher controls the timing of the stretching and contractions.