Orthostatic-dependent cardiopulmonary responses among trained females during intensity matched resistance exercises in a pilot randomized crossover study

Abstract

The impact of orthostatic regulation during exercise, particularly resistance training, is not fully understood. This study investigates the acute cardiopulmonary responses of intensity-matched resistance exercises, targeting similar muscle groups but performed in different body positions in young trained females. Fourteen healthy females (21.6 ± 2.0 years) performed a 3-repetition Maximum test (3-RM) for the squat movement in the Smith machine (SM) and the leg press (LP). During two subsequent visits, they randomly completed two training sessions in SM and LP (two sets of ten repetitions at 50% 3-RM). Blood pressure (vascular unloading technique) and cardiopulmonary parameters (impedance cardiography, spirometry) were measured continuously. At baseline, there was a significant difference in heart rate and stroke volume between the SM and LP conditions. During training sessions, the SM condition showed higher ground reaction force (986.9 ± 93.3 vs. 811.2 ± 71.6 N; p < .01), systolic blood pressure (156 ± 15 vs. 141 ± 10 mmHg; p < .01), diastolic blood pressure (111 ± 11 vs. 96 ± 8 mmHg; p < .01), HR (123 ± 11 vs. 97 ± 7 bpm; p < .01), and oxygen uptake (901 ± 104 vs. 623 ± 65 ml/min; p < .01) compared to the LP condition. Total peripheral resistance (TPR) was similar. Significant different post-exercise changes could be detected in mean arterial pressure (-20.9 ± 9.9 vs. 3.3 ± 11.0 mmHg; p < .01) and TPR (-2.3 ± 1.7 vs. 0.7 ± 1.7 mmHg⋅ l⋅min-1; p < .01). Squats in the SM require greater cardiovascular and pulmonary effort than matched exercising in LP due to orthostatic stress and higher muscle activation. Conversely, the risk of blood pressure peaks is much lower with LP. Future analysis should focus on the effects of body position on patient responses.