Thermotherapy associated with flexibility training does not increase the knee range of movement of healthy adults: systematic review and meta-analysis of randomized clinical trials

The stretching with thermotherapies associated have been related in the literature as a way to increase the range of motion (ROM), but still are not consensus about this efficacy and cost-effectiveness. The muscle stretching is a useful technique in rehabilitation and in physical activities programs, either to gain or maintain the flexibility, as a recovery of musculoskeletal and joint injuries. Objective: To determine the effects of thermotherapies associated to flexibility training in ROM of knee extension in healthy adults. Method: The search strategy was conducted in main databases, as Cochrane Library, LILACS, PEDro, PUBMED/ Medline, Scopus and Web of Science. The searches were done in 2016, and renewed in 2023, in order to achieve new publications along this time. Were selected only randomized clinical trials that have executed a training of hamstrings stretching, associated or not with one or more thermotherapies in healthy young adults, as long as the outcome was knee extension ROM. Only papers in Portuguese or English were assessed. To evaluate risk of bias was used the Cochrane Collaboration’s Risk of Bias Tool, and the methodological quality assessment was rated following the PEDro Scale. Results: Eight articles were included, totalizing 260 participants. The papers showed low methodological quality, and uncertain risk of bias. Only chronic effect of local warming and cryotherapy plus stretching showed a statistically significant difference versus control group. However, the thermotherapy action associated with stretching is still unclear, once the results suggest that even without the thermotherapy there are ROM increases. Conclusion: The stretching is effective in knee extension ROM improvement in healthy adults, with or without thermotherapy. New studies with higher methodological rigor and standardized protocols are needed.