Form influences function: anthropometry and orthostatic stability during sustained acceleration in a short arm human centrifuge

Introduction: The goal of this study was to determine which anthropometric factors measured via air displacement plethysmography (ADP) play a significant role in augmenting orthostatic stability during sustained acceleration G-force (þG) exposure in a short arm human centrifuge (SAHC). The authors hypothesized that test subjects with a greater normalized fat free mass in percentage of total body mass (FFM%) would exhibit greater orthostatic stability during consecutive þG loads. Methods: Twenty þG naive test subjects (10 female, 10 male), were recruited for this study, in which they underwent 2 rounds of 1/2/1 G-force profile in a SAHC. Before being exposed to þG, each subject underwent anthropometric analysis via ADP to ascertain total body mass (BM, kg), body volume (BV, L), body surface area (BSA, m2 ), normalized fat mass/fat free mass in percentage of total body mass (FM% and FFM%). During SAHC exposure, hemodynamic parameters were continuously obtained from each test subject. The measured anthropometric parameters were compared against baseline mean arterial pressure (MAP, mmHg), heart rate (HR, bpm), stroke volume (SV, mL) cardiac output (CO, L min1 ) and systemic vascular resistance (SVR, dyn s cm5 ) to determine correlations. Results: From the 20 subjects, 13 test subjects (5 F, 8 M) completed all phases of þG exposure, and were therefore classified as having high þG tolerance (NALOC). From the 7 remaining test subjects (5 F, 2 M); 6 aborted or reduced their þG exposure, and were therefore classified as exhibiting low þG tolerance (ALOC). One subject dropped out prior to testing, and is not included in the data. Total BM, BV, and BSA were significantly higher (po0.05) in the NALOC group. Significant correlations between baseline SV/CO and these parameters were also determined. FFM% showed no differences between the two groups, and did not exhibit any correlations with baseline hemodynamics. NALOC subjects tended to have a higher CO and SV at baseline, whereas ALOC subjects tended to exhibit higher SVR at baseline. Discussion: Total BM, BV, and BSA were the anthropometric factors associated with orthostatic stability during þG. The higher these parameters, the higher the baseline SV, which combined contributed to greater orthostatic stability during þG. Male test subjects had an overall