Kinematics and muscle activation of the lower limb during barefoot and flip-flop running

Flip-flop and barefoot running are increasingly common; however, their biomechanical effects remain unclear. This study examined lower-limb kinematics and muscle activation during treadmill running under barefoot, conventional flip-flop, Y-Sandal, and shod conditions. Sixteen volunteers were recruited to run on a treadmill under four footwear conditions at three speeds. A three-dimensional motion capture system was used to collect kinematic data, and the activities of the tibialis anterior, extensor digitorum longus, and flexor hallucis longus muscles were simultaneously recorded using a wireless electromyography system. Barefoot running was associated with higher cadence, whereas the Y-Sandal condition was associated with the shortest stance duration. The conventional flip-flop condition was associated with greater sagittal-plane hip motion compared with the Y-Sandal and shod conditions. The barefoot and conventional flip-flop conditions were associated with similar ankle and forefoot movement patterns in sagittal and frontal planes, whereas the Y-Sandal and shod conditions produced different patterns. Furthermore, significantly higher lower-leg muscle activation was observed under the conventional flip-flop and Y-Sandal conditions compared with the barefoot and shod conditions. Footwear design significantly affects running biomechanics and neuromuscular strategies. Although barefoot running promotes a higher cadence, thong-style footwear increases the demand on the distal musculature. The specific design features of the Y-Sandal appear to mitigate the compensatory kinematic strategies typically observed with conventional flip-flops, resulting in movement patterns that more closely resemble those observed during shod running. These findings highlight the distinct neuromuscular demands and kinematic adaptations associated with different footwear interfaces.