IASTM vs. Static Stretching for Hamstring Tightness: Short- and Long-Term Effects (IASTM-HT)

Hamstring muscle tightness is a common musculoskeletal condition that can limit hip and knee range of motion, reduce athletic and functional performance, and contribute to other conditions such as patellofemoral pain, patellar tendinopathy, and low back pain. Static stretching has long been used to address hamstring tightness, with systematic reviews suggesting that 6-8 weeks of regular stretching can produce lasting flexibility gains. Instrument-assisted soft tissue mobilization (IASTM) has more recently emerged as an alternative technique, with proposed mechanisms including controlled microtrauma that stimulates an inflammatory response and collagen remodeling in soft tissue.

Most existing studies comparing static stretching and IASTM for hamstring tightness have examined only single-session or short-term (immediate post-treatment) effects. Long-term follow-up data (≥8 weeks) are limited, making it difficult to determine whether treatment-related gains in flexibility, pain sensitivity, and functional performance are sustained over time.

This randomized controlled trial will enroll 46 participants with hamstring tightness, defined as hip flexion range of motion <65° on the Straight Leg Raise (SLR) test with no neurological signs. Participants will be randomly allocated (computer-generated randomization) to one of two equal groups (n=23 each):

Group 1 (IASTM): Participants will receive instrument-assisted soft tissue mobilization applied to the hamstring muscle group using a stainless-steel instrument, scanning technique, distal-to-proximal direction, for 5 minutes per session.

Group 2 (Static Stretching): Participants will receive manual static stretching of the hamstring muscle group, performed in 5 repetitions of 30 seconds of stretch followed by 30 seconds of rest (5 minutes total per session).

Both interventions will be delivered 3 times per week for 4 weeks (12 sessions total) by a physical therapist with over 10 years of clinical experience in orthopedic rehabilitation and manual therapy.

Outcome assessments will be performed by a blinded assessor independent of treatment delivery, at three time points: baseline (pre-treatment), short-term (3 days after the final session), and long-term (8 weeks after intervention completion). Outcome measures include:

• Flexibility: knee extension range of motion during 90° hip flexion, measured with a digital inclinometer
• Pressure pain threshold: measured with a digital algometer over the hamstring muscle bellies (biceps femoris, semitendinosus, semimembranosus)
• Functional performance: vertical jump height and single-leg hop distance

Statistical analysis will include two-way repeated-measures ANOVA to assess time and group-by-time interaction effects, with Bonferroni-corrected post hoc comparisons where appropriate.