Flexibility is one of the key components of health-related physical fitness and is influenced by various factors such as age, gender, joint structure, and muscle anatomy. Hamstring tightness can contribute to multiple lower extremity injuries. While traditional methods like stretching and myofascial release are commonly used to improve flexibility, instrument-assisted soft tissue mobilization (IASTM) has recently gained popularity. However, no studies in the current literature have compared the acute effects of these three methods in individuals with hamstring tightness. This study aims to compare the acute effects of stretching, myofascial release, and IASTM in individuals diagnosed with hamstring tightness (defined as <65° of hip flexion in the straight leg raise test without neurological findings).

Hamstring tightness is a common musculoskeletal problem that can contribute to lower extremity injuries and functional limitations. Flexibility, one of the fundamental components of physical fitness, can be influenced by multiple factors including age, sex, joint structure, and muscle properties. Among various therapeutic approaches, static stretching and myofascial release are conventionally used to improve hamstring flexibility. More recently, instrument-assisted soft tissue mobilization (IASTM) has gained popularity for its potential to increase range of motion and reduce muscle tension more rapidly than traditional methods.

The study aims to identify which intervention is most effective in increasing hamstring flexibility acutely and will provide evidence to guide clinical decision-making in sports rehabilitation and injury prevention. Additionally, this research intends to fill a gap in the literature, as no prior study has directly compared these three methods in individuals with hamstring tightness.

This study is designed as a prospective, randomized, controlled, double-blind trial to compare the acute and short-term effects of three different manual therapy interventions such as static stretching, self-myofascial release using a vibrating foam roller, and IASTM on individuals with clinically diagnosed hamstring tightness. A fourth group will serve as the control group and will receive no intervention.

A total of 36 healthy participants, aged 18 to 30 years, with hamstring tightness confirmed via the Straight Leg Raise (SLR) test (hip flexion <65° without neurological findings), will be randomly assigned into one of four groups. Each group will consist of 9 participants. Interventions will be applied for approximately 5 minutes. Assessments will be conducted at four time points: baseline (pre-intervention), immediately after intervention, 12 hours post-intervention, and 24 hours post-intervention.

Inclusion Criteria:

• Age between 18 and 30 years
• Presence of hamstring tightness (Straight Leg Raise angle < 65°)
• No diagnosed chronic diseases
• Voluntary participation and signed informed consent

Exclusion Criteria:

• History of lower extremity trauma or surgery
• Symptoms radiating to one or both legs due to hamstring, spinal, or sciatic nerve injury
• Ankle instability
• Neurological findings during the straight leg raise test
• Presence of hyperalgesia, hematoma, varicose veins, or skin infection in the lower limb