Effects of Combining PNF With NMES in Young Football Players (PNF+NMES)

Cardenal Herrera University

Status: Completed

Conditions: Hamstring Muscle Tightness; Hamstring Flexibility

Treatments: Other: Contract-Relax PNF (crPNF); Other: Sham Neuromuscular electrical stimulation (NMES); Other: Neuromuscular electrical stimulation (NMES)

Study type: Interventional

Funder types: Other

Identifiers

NCT07075497

UNIVERSITY CARDENAL HERRERA-97

Details and patient eligibility

About

Hamstring muscle injuries are common in sports like football and often lead to extended periods of inactivity. This study aims to compare the effects of two different stretching programs on hamstring flexibility, with a secondary focus on jumping performance in young football players. One group will perform a proprioceptive neuromuscular facilitation (PNF) stretching protocol combined with neuromuscular electrical stimulation (NMES), while the other group will follow the same PNF protocol with a placebo NMES.

Full description

Hamstring strains are increasingly common in sports, particularly in football, where they are among the most frequent injuries. Stretching techniques such as proprioceptive neuromuscular facilitation (PNF) are commonly used to improve muscle flexibility and reduce injury risk. A specific variant, contract-relax PNF (crPNF), involves alternating passive stretching with voluntary muscle contractions. Recent approaches suggest that applying neuromuscular electrical stimulation (NMES) during the contraction phase of crPNF may further enhance its effectiveness.

This study aims to compare the short-term effects of two active stretching protocols on hamstring flexibility in young male football players. One group will perform crPNF with sham NMES, while the other will perform crPNF with NMES during the contraction phase. A secondary objective is to assess whether either protocol affects vertical jump performance, a key ability in football.

Enrollment: 47 patients

Sex: All

Ages: 10 to 18 years old

Volunteers: Accepts Healthy Volunteers

Inclusion criteria

• Active football players who train at least 3 days a week.
• Ages between 10 and 18 years.

Exclusion criteria

• Are currently engaged in a structured hamstring-stretching programme.
• Present with acute low back pain.
• Have sustained a hamstring injury within the past 6 months.
• Have undergone spinal or abdominal surgery within the past 6 months.

Trial design

Primary purpose: Treatment

Allocation: Randomized

Interventional model: Parallel Assignment

Masking: Single Blind

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47 participants in 2 patient groups, including a placebo group

contract-relax proprioceptive neuromuscular facilitation with sham NMES (crPNF + sham NMES)

Placebo Comparator group

Description:

Participants sat in long-sitting with maximal knee extension and pelvic anteversion controlled by elastic straps over the pelvis and distal thigh. Two 5×5 cm self-adhesive electrodes were placed on the hamstrings: one two fingerbreadths below the gluteal fold (proximal) and one over the distal third of the muscle belly. Sham NMES delivered biphasic symmetric rectangular pulses (50 Hz, 250 µs) at the sensory threshold (minimal intensity eliciting only a slight tingling without visible muscle response). Each of three cycles comprised a 10 s maximal voluntary isometric hamstring contraction ("Squeeze…!") against the fixed table, immediately followed by a 30 s passive stretch to a moderate-strong but non-painful tension ("Stretch…!"). A primary researcher ensured consistent limb positioning and strap tension; a secondary researcher monitored timing and cued contractions by lightly supporting the heels.

Treatment:

Other: Contract-Relax PNF (crPNF)

Other: Sham Neuromuscular electrical stimulation (NMES)

Neuromuscular Electrical Stimulation (NMES + crPNF)

Experimental group

Description:

Participants sat in long-sitting with maximal knee extension and pelvic anteversion controlled by elastic straps over the pelvis and distal thigh. Two 5×5 cm self-adhesive electrodes were placed on the hamstrings: one two fingerbreadths below the gluteal fold (proximal) and one over the distal third of the muscle belly. NMES delivered biphasic symmetric rectangular pulses (50 Hz, 250 µs) at each participant's maximal motor threshold without discomfort or pain; the resulting milliamperage was recorded for each leg and used during all contraction phases. Each of three cycles comprised a 10 s maximal voluntary isometric hamstring contraction ("Squeeze…!") with NMES applied at the recorded intensity, immediately followed by a 30 s passive stretch to a moderate-strong but non-painful tension ("Stretch…!"). A primary researcher ensured consistent limb positioning and strap tension; a secondary researcher monitored timing and cued contractions by lightly supporting the heels.

Treatment:

Other: Neuromuscular electrical stimulation (NMES)

Other: Contract-Relax PNF (crPNF)