Objective: The influence of backrest support and handgrip contractions on acute metabolic, respiratory, and cardiovascular responses were evaluated in 13 healthy men during exposure to whole-body vibration (WBV).
Methods: Following assessment of aerobic fitness during arm cranking, subjects were exposed to frequencies 3, 4.5, and 6 Hz with 0.9 g(r.m.s) acceleration magnitude on a vibrating base in randomized order, on separate days. Each exposure included 6 min baseline without WBV, 8 min of WBV exposure either 'with' or 'without' backrest, 4 min recovery, followed by 8 min of WBV with opposite backrest condition, and 4 min recovery. During the final minute of WBV, subjects performed right hand maximal rhythmic handgrip contractions for one minute. During baseline and before completion of WBV session 'with' and 'without' backrest, cardiac output was estimated indirectly by carbon dioxide rebreathing.
Results: At 3 and 4.5, and 3 and 6 Hz, absolute and relative oxygen uptake demonstrated significantly greater responses during sitting 'without' backrest than 'with' backrest (P<0.01). At 3 and 4.5 Hz, heart rate and oxygen pulse responses were significantly greater during WBV combined with handgrip contractions than during WBV alone (P<0.01), demonstrating physical work during WBV will enhance greater metabolic responses. Stroke volume was the lowest at 4.5 Hz (P<0.01). Influence of aerobic fitness was evident only in absolute oxygen uptake, oxygen pulse, and ventilation volume (P<0.01).
Conclusions: This study demonstrates that subjects exposed to physical work during WBV will experience greater metabolic responses compared to WBV alone, and the physiological responses during WBV resemble to that of a light physical work. Despite low metabolic rates during WBV, the effect of aerobic fitness suggests the importance of physical activity in occupations exposed to WBV.