Effects of age and fitness on tolerance to lower body negative pressure

Background. The purpose of this investigation was to determine the effects of age and fitness on tolerance to maximal lower body negative pressure (LBNP). Methods. Ten older fit (OF) 73.9 +/- 2 years 39.0 +/- 2 ml.kg(-1).min(-1) (age and estimated VO(2)peak, respectively), 10 older unfit (OU) (70.9 +/- 1 years; 27.1 +/- 2 ml-kg(-1)min(-1)), 10 young fit (YF)(22.6 +/- 0.5 years, 57.1 +/- 2 ml.kg(-1) min(-1)), and 10 young unfit (YU) (23.1 +/- 1 years; 41.1 +/- 2 ml.kg(-1)min(-1)) participants underwent graded LBNP of -10 mmHg every 4 minutes to either presyncope or -100 mmHg. Results. Compared to the other groups, YF had an earlier increase in heart rate (-40 mmHg vs the last stage YFvs OF, OU, and YU, respectively) and decline in stroke volume (-20 mmHg vs -40 mmHg; YF vs OF, OU, and YU. respectively). OU had a higher resting mean arterial pressure: this difference was maintained until the last stage. OF had an earlier decline in total peripheral conductance than the other groups (-20 mmHg vs -40 mmHg), Tolerance to maximal LBNP did not differ among the groups. Conclusions. Despite differences in the responses to submaximal LBNP, neither age nor cardiovascular fitness affect tolerance to maximal LBNP.