Acute Effects of Proprioceptive Neuromuscular Facilitation on Hamstring-to-Quadriceps Strength Ratio

The present study investigated the acute effects of two commonly used stretching modalities-proprioceptive neuromuscular facilitation (PNF) and static stretching-on isokinetic muscle strength and hamstring-to-quadriceps (H/Q) ratios in physically active healthy young males. The study employed a randomized crossover design with repeated measures, allowing each participant to complete both experimental conditions under standardized laboratory settings.

Participants attended three sessions: a familiarization session followed by two experimental sessions separated by at least 48 hours. Each experimental session included a standardized warm-up, followed by either PNF or static stretching intervention, and subsequent isokinetic strength testing. Peak torque values for quadriceps (concentric) and hamstrings (concentric and eccentric) were measured using an isokinetic dynamometer at 60°/s. Traditional and functional H/Q ratios were calculated.

The primary aim was to determine whether these stretching modalities produce acute alterations in muscle strength and H/Q ratios. The study also examined whether the type of ratio (traditional vs. functional) significantly influences outcomes. Findings contribute to understanding the neuromuscular implications of stretching in warm-up protocols.

• PNF Stretching (Other): Participants performed four repetitions of PNF stretching consisting of a 6-second isometric hamstring contraction at approximately 60% of maximal voluntary contraction followed by a 30-second passive stretch. Rest intervals were standardized.
• Static Stretching (Other): Participants performed four repetitions of static hamstring stretching, each lasting 30 seconds, with 30-second rest intervals between repetitions.

Primary outcomes

• Hamstring-to-Quadriceps (H/Q) Ratio [Immediately after intervention]: Both traditional (Hcon/Qcon) and functional (Hecc/Qcon) ratios were calculated using isokinetic peak torque values.

Secondary outcomes

• Quadriceps Concentric Peak Torque [Immediately post-intervention]: Quadriceps Concentric Peak Torque
• Hamstring Concentric Peak Torque [Immediately post-intervention]: Hamstring Concentric Peak Torque
• Hamstring Eccentric Peak Torque [Immediately post-intervention]: Hamstring Eccentric Peak Torque

Sex: Male, ages: 18 Years to 25 Years, accepts healthy volunteers

Inclusion Criteria:

* Age between 18 - 25 years, healthy male individuals
* Physically active (≥3 days/week, ≥30 min/day)

Exclusion Criteria:

* Musculoskeletal injury in the last 6 months
* Any neurological or orthopedic disorder