Objective: Stretching and warm-up exercises are commonly used to increase hamstring flexibility in sports rehabilitation. The aim of the study was to compare immediate and short-term effects of hot packs, infrared, and ultrasound on hamstring flexibility when ap-plied before stretching exercises in healthy individuals.
Materials and Methods: A total of 60 participants were randomly divided into four groups. All participants performed hamstring stretching exercise three times a week for six weeks. Each stretching session consisted of three repetitions of 15 seconds duration. Before the stretching exercises, hot packs were applied to Group I, infrared to Group II, and ultrasound to Group III. Group IV (control group) performed self-stretching exercises alone. Hamstring flexibility was as-sessed with the Active Knee Extension (AKE) test in all sessions before and after the interventions.
Results: AKE significantly increased after all sessions (p<0.05) and in the short term (p<0.05) in all groups. The short-term effect did not differ between the groups (p>0.05). Among the different agents, infrared has the highest effect size.
Conclusion: The results of the study showed that both superficial and deep heat agents had an increasing effect on hamstring flexibility. However, the application of superficial or deep heat agents before stretching exercises did not provide an additional increase in hamstring flexibility.