Effects of calcium-regulating pulsed electromagnetic field combined with low-load blood flow restriction training on strength and performance adaptations in adolescent sprinters

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Background: When recovery capacity is limited during the competitive season, low-load blood flow restriction training (LL-BFR) is increasingly used as an alternative to high-load resistance training (HL-RT). This study examined whether combining calcium-regulating pulsed electromagnetic field (Ca-R-PEMF) with LL-BFR further enhances maximal strength and its transfer to jumping and anaerobic performance. Methods: Forty-six adolescent sprinters were randomly assigned to high-load resistance training [80% one-repetition maximum (1RM)], LL-BFR [30% 1RM; 30-15-15-15 repetitions; cuff pressure = 80% limb occlusion pressure], or Ca-R-PEMF + LL-BFR. All groups completed three sessions per week for four weeks. The primary outcome was 1RM, and secondary outcomes included lower-limb maximal voluntary isometric contraction (MVIC), jumping performance, and 30-s Wingate-derived outcomes. Between-group effects were analyzed using baseline-adjusted ANCOVA. Results: After baseline adjustment, a significant between-group effect was observed for 1RM. HL-RT produced greater gains than LL-BFR (Adjusted Mean Difference = 12.20 kg, 95% CI: 4.11 to 20.29; p = 0.002), while Ca-R-PEMF + LL-BFR did not differ statistically from HL-RT (p = 0.243). For knee extensor MVIC, Ca-R-PEMF + LL-BFR exceeded LL-BFR (p = 0.033) and did not differ statistically from HL-RT; for plantar flexor MVIC, Ca-R-PEMF + LL-BFR exceeded HL-RT (p = 0.005). Squat jump height improved more with Ca-R-PEMF + LL-BFR than LL-BFR (p = 0.017), whereas no clear between-group effects were observed for countermovement jump height or standing broad jump distance. Wingate peak power was higher with Ca-R-PEMF + LL-BFR than LL-BFR (p = 0.011), while both BFR conditions showed lower fatigue indices than HL-RT. Conclusion: Over four weeks, Ca-R-PEMF + LL-BFR did not differ statistically from HL-RT for 1RM, and improved selected isometric strength measures, jump, and 30-s Wingate-derived outcomes compared with LL-BFR alone, without increasing external load in adolescent sprinters. Trial registration: Chinese Clinical Trial Registry (ChiCTR2300078947). Ethics approval was granted by the Bioethics and Medical Ethics Committee of Northeastern University (NEU-EC-2025B069).

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