Different Time Course of Recovery in Achilles Tendon Thickness After Low-Load Resistance Training With and Without Blood Flow Restriction

CONTEXT Blood flow restriction research has focused on muscular strength and hypertrophy. Limited data have been reported about the blood flow restriction effect on the tendon. OBJECTIVE To analyze and compare the time course of recovery in Achilles tendon thickness after a single bout of low-intensity resistance training (LI-RT) and low-intensity blood flow restriction training (LI-BFRT). METHODS A total of 56 healthy participants (24.60 [4.0] y; 23.65 [3.4] body mass index) were included. The dominant leg was assigned for LI-BFRT using low load (30% 1-repetition maximum) and 30% of the total occlusion pressure (52.21 [17.89] mm Hg) in plantar-flexion exercise (1 × 30 + 3 × 15 repetitions). The nondominant leg was assumed as a control condition. MAIN OUTCOME MEASURE Sonography images were taken before the intervention, immediately posttraining, and 24 hours after exercise (post-24) for the Achilles tendon thickness. RESULTS Changes in Achilles tendon thickness for LI-BFRT group were significant post- (-14.5%; P < .05) and post-24 (-9.2%; P < .05). In contrast, LI-RT group showed a transient decrease after exercise (-9.67%; P < .05) followed by a recovery of thickness post-24 (-1.06%; P < .05). Thickness post-24 was different between LI-BFRT versus LI-RT (P < .01). Hedge effect size analysis showed a large effect (g = 0.90) in LI-BFRT pre-post condition and a medium effect (g = 0.57) in post- to post-24. The LI-RT obtained a medium effect (g = 0.53) in pre-post condition and a small effect (g = 0.49) in post- to post-24. CONCLUSIONS This study showed a different time course of the acute response in Achilles tendon thickness between LI-BFRT and LI-RT. This may be associated with intratendinous fluid movement in response to LI-BFRT.