Effects of Low-Level Laser Therapy on HSP70 Dynamics and Recovery Biomarkers in Elite Athletes: A Multi-Sport Longitudinal Investigation

Background: Photobiomodulation therapy (PBMT), also called low-level laser therapy (LLLT), has gained traction as a legal, non-invasive recovery tool in sport. Meta-analyses of 39 randomized controlled trials confirm its ergogenic potential for muscular performance and fatigue reduction. Heat shock protein 70 (HSP70), a stress-responsive molecular chaperone central to proteostasis, rises predictably after exercise in animal models - yet its dynamics remain poorly mapped in longitudinal human athletic cohorts. To date, only one study (Evangelista et al., 2021) has examined LLLT effects on HSP70, and that work used a rat tendinitis model. No human data exist. Methods: We conducted a multi-sport longitudinal investigation (2010-2018) involving approximately 90 athletes across five disciplines: swimming (n = 48), rowing (n = 17), wrestling (n = 8), gymnastics (n = 20), and marathon running (n = 6). The LLLT protocol consisted of transcutaneous polyzonal infrared laser stimulation (808-904 nm, < 100 mW/cm²), administered over 6-8 sessions across two weeks. Serum HSP70 was quantified using a custom sandwich ELISA with recombinant hexahistidine-tagged HSP70 standards. Additional biomarkers included creatine kinase (CK), cortisol, testosterone, malondialdehyde (MDA), and HSP-family mRNA expression via RT-PCR. Results: Athletes receiving LLLT showed a +5.7% improvement in mean swimming velocity (p < 0.05), an effect that persisted for 1-1.5 months after treatment cessation. HSP70 increased 1.8-fold following aerobic loading (p < 0.05) but did not change after short anaerobic efforts. Basal HSP70 concentrations above 14-15 ng/ml during recovery periods signaled overtraining risk. Sport-specific differences were dramatic: preparatory-phase HSP70 in gymnasts averaged 64.2 ng/ml compared with 11.5 ng/ml in rowers. No correlation was found between HSP70 and MDA or between HSP70 and CK. Conclusions: This study provides the first human evidence of LLLT-associated performance gains alongside concurrent HSP70 monitoring in athletes. HSP70 emerges as a viable, sport-specific biomarker for detecting overtraining before clinical symptoms manifest.