Simulated hypergravity running increases skeletal and cardiovascular loads

Eight recreational and eight competitive athletes were studied to determine the cardiovascular and musculoskeletal effects of running in hypergravity conditions simulated by the use of lower body negative pressure (LBNP). Subjects are sealed in a LBNP chamber with the use of a flexible, neoprene waist seal and the chamber pressure is reduced to provide an increased vertical force. Subjects ran on a treadmill at 1.0, 1.1, and 1.2 times body weight (BW) with increased loads provided by LBNP. Heart rate (HR), oxygen consumption (VO(2)), vertical ground reaction force (GRF), dynamic knee range of motion (ROM), and the electrical activities (EMG) of the tibialis anterior, medial gastrocnemius, vastus medialis obliquous, and biceps femoris muscles were measured. LBNP produced a significant increase in HR at the 1.1-BW and 1.2-BW levels in both recreational and competitive athletes when compared with the 1.0 BW condition. Both VO(2) and GRF were increased significantly at 1.2 BW. No significant changes were observed in knee ROM or peak EMG amplitude with LBNP in either recreational or competitive athletes. Increased HR and VO(2) indicate an increased cardiovascular load whereas increased GRF indicates an increased skeletal load. The lack of change in muscle activation and knee ROM point to a preservation in gait mechanics. Increased cardiovascular and skeletal loads with preservation of gait mechanics suggest that exercise within LBNP may be an effective training modality to improve athletic performance.