Effects of Different Exercises during 90-Day Head-Down Tilt Bed Rest on Post-Bed Rest Walking Gait

Background: Head-down bed rest (HDBR) is a common method for simulating microgravity. Prolonged HDBR leads to adaptive changes in gait cycle, joint angle, and muscle activation. These changes may affect the efficiency and stability of daily activities and task execution. Therefore, it is necessary to optimize current exercise training protocols to maintain astronauts' ability to perform critical tasks and extend mission duration.
Objective: To investigate the effects of HDBR and different exercise training on walking gait biomechanics and lower limb muscle activation.
Methods: Thirty-six participants underwent a 90-day HDBR and were randomly divided into five groups: Group A (control group, 8 participants, no exercise training), Group B (7 participants, HDBR + aerobic training), Group C (7 participants, HDBR + high-load resistance training), Group D (7 participants, HDBR + aerobic training + low-load resistance training), and Group E (7 participants, HDBR + aerobic training + high-load resistance training). Gait and surface electromyography analysis were conducted 1 day before bed rest, 3 day after getting up, and 24 day after getting up.
Results: 1) Test time significantly affected single support phase, double support phase, swing phase, step rate, min and max hip angles, min and max knee angles, knee range of motion (ROM), min and max ankle angles, and activation of major lower limb muscles (P < 0.05). 2) Group significantly influenced stance phase, step rate, step length, walking speed, min ankle angle, ankle ROM, lateral gastrocnemius activation, and soleus activation (P < 0.05).
Conclusion: 1) Adaptive changes in walking gait were characterized by increased support phase, decreased swing phase, and reduced step rate, reflecting changes in motor control strategies. 2) Exercise training interventions primarily improved ankle motion and enhanced activation of calf muscles, but had limited effects on hip and knee motion as well as thigh muscle activation. Among all training protocols, high-load resistance training was crucial for maintaining and recovering lower limb walking gait, especially when combined with aerobic training. 3) Recovery effects indicated that lower limb motor control had not recovered to previous level in 24 day after getting up, but ankle recovered faster than hip and knee.