Abstract-We compared the test-retest reliability of nearinfrared spectroscopy (NIRS) measures of cerebral oxygenation and blood volume during a rhythmic handgrip exercise in 13 nondisabled subjects and 25 subjects with moderate to severe traumatic brain injury (TBI). Subjects with TBI (average Glasgow Coma Scale score = 4.2, average time since injury = 21 mo) had completed an acute brain injury rehabilitation program. After 2 min of rest, each subject performed 60 s of maximal rhythmic handgrip contractions with the right hand in two trials 24 to 48 h apart. We used NIRS to measure cerebral oxygenation and blood volume responses from the left prefrontal lobe. Both groups' cerebral oxygenation and blood volume increased during handgrip contractions. The change in cerebral oxygenation was significantly lower in subjects with TBI compared with nondisabled subjects. Intraclass correlations between the two trials for cerebral oxygenation and blood volume were 0.83 and 0.80, respectively, in nondisabled subjects and 0.70 and 0.64, respectively, in subjects with TBI. The findings indicate that NIRS is a reliable noninvasive technique for evaluating cerebral oxygenation and blood volume changes during motor function. NIRS can be useful in monitoring recovery of cerebral oxygenation during rehabilitation of patients with TBI.

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The purpose of this study was to compare the rates of muscle deoxygenation in the exercising muscles during incremental arm cranking and leg cycling exercise in healthy men and women. Fifteen men and 10 women completed arm cranking and leg cycling tests to exhaustion in separate sessions in a counterbalanced order. Cardiorespiratory measurements were monitored using an automated metabolic cart interfaced with an electrocardiogram. Tissue absorbency was recorded continuously at 760 nm and 850 nm during incremental exercise and 6 min of recovery, with a near infrared spectrometer interfaced with a computer. Muscle oxygenation was calculated from the tissue absorbency measurements at 30%, 45%, 60%, 75% and 90% of peak oxygen uptake (VO2) during each exercise mode and is expressed as a percentage of the maximal range observed during exercise and recovery (%Mox). Exponential regression analysis indicated significant inverse relationships (P < 0.01) between %Mox and absolute VO2 during arm cranking and leg cycling in men (multiple R = -0.96 and -0.99, respectively) and women (R = -0.94 and -0.99, respectively). No significant interaction was observed for the %Mox between the two exercise modes and between the two genders. The rate of muscle deoxygenation per litre of VO2 was 31.1% and 26.4% during arm cranking and leg cycling, respectively, in men, and 26.3% and 37.4% respectively, in women. It was concluded that the rate of decline in %Mox for a given increase in VO2 between 30% and 90% of the peak VO2 was independent of exercise mode and gender.

In this study, we compared the biomechanical and physiological responses of healthy men and women during bilateral load carriage while they walked on a treadmill at their self-selected velocity. Eleven men mean (SD) maximal oxygen uptake, [VO(2)(max) = 56.0 (7.1) ml x kg(-1) x min(-1)] and 11 women [VO(2)(max) = 44.6 (7.6) ml x kg(-1) x min(-1)] carried 15-kg and 20-kg loads in random order using a custom-designed load-carriage device. The load supported by each hand was measured by placing strain gauges in each handle of the device. The load supported by the body was calculated as the difference between the load carried and that supported by each hand. Physiological measurements were recorded using standard procedures, and cardiac output was measured by carbon dioxide rebreathing while standing, walking, and during load carriage. Three-way analysis of variance (gender by load by test phase) indicated no significant (P > 0.05) three-way interaction, implying that the overall trend in these responses was similar in men and women. A-priori Scheffe multiple comparisons revealed the following significant (P < 0.05) gender differences during load carriage: (1) women supported a lower proportion of the load with the hands and transferred a greater amount to the body by resting the load against the chest, (2) the oxygen uptake increased by a greater amount in the women compared with men and exceeded the ventilatory threshold during the 20-kg walk in women, and (3) the cardiovascular stress, as indicated by the percentage of maximal heart rate and rate pressure product (product of heart rate and systolic blood pressure), was significantly higher in women compared with men during both of the load-carriage walks. These observations suggest that when carrying absolute loads of 15 kg and 20 kg, women are more susceptible to fatigue and are at a greater risk of cardiovascular complications than men.