Comparative Effects of Circuit Training, High-Intensity Interval Training, and Combined Training on Performance and...

Panthong, S, Tongsiri, N, Tanaka, H, and Suksom, D. Comparative effects of circuit training, high-intensity interval training, and combined training on performance and neuromuscular function in masters trail runners. J Strength Cond Res XX(X): 000-000, 2026-Middle-aged trail runners often face time constraints due to occupational and family responsibilities, and many lack regular access to terrain-specific environments. Therefore, time-efficient training modalities capable of replicating the physiological and biomechanical demands of trail running are warranted. This study compared the effects of 3 such training modalities on performance and neuromuscular adaptations in master trail runners. Forty runners aged 35-55 years were randomly assigned to circuit weight training (Circuit: n = 13), uphill-high intensity interval training (HITT: n = 13), or combined training (n = 14) for 12 weeks. All groups performed 3 endurance sessions per week in addition to 3 modality-specific sessions. Outcomes included mountain trail running time, running economy during level and uphill running, maximal oxygen consumption (V̇O2max), anaerobic fitness, lean mass, knee extensor strength, countermovement jump power, leg stiffness, dynamic balance, and neuromuscular function. Mountain trail performance improved following HIIT and combined training (p < 0.05). Circuit and combined training increased lean mass, muscle strength, jump power, and maximal voluntary contraction (p < 0.05), whereas voluntary activation remained unchanged. Running economy during level and uphill running improved in HIIT and combined groups (p < 0.05). V̇O2max, anaerobic fitness, leg stiffness, and balance improved across all groups (p < 0.05). Overall, HIIT and combined training were more effective in enhancing uphill running economy and trail performance, while combined training provided complementary neuromuscular and endurance adaptations. These findings support multimodal strategies as time-efficient approaches to optimize performance in master trail runners.