Determination of young adults' sedentary time with a multisensory activity monitor and activity log diary.

BACKGROUND: Quantification of sedentary time still remains a challenge. OBJECTIVES: This study examined: 1) whether a multisensory activity monitor could accurately measure sedentary activities and discriminate them from light intensity activities; and 2) the validity of activity log diary (AL) in estimating sedentary time using the monitor as a criterion measure. METHODS: Thirty healthy individuals performed sedentary and light intensity activities in a laboratory while being equipped with a metabolic measurement cart (MMC) and the multisensory monitor. Subsequently, a subset of 19 participants completed AL while wearing the monitor for three days under free-living conditions. RESULTS: Metabolic equivalents (METs) measured by the multisensory monitor during sedentary activities were similar to those measured by MMC and were significantly lower than light-intensity activities (p < 0.001). Relative criterion validity of AL assessed by Pearson's correlation coefficient was high (r = 0.68, p < 0.01). Absolute criterion validity examined by Bland-Altman plots showed small mean difference between AL and the monitor (36.9 minutes ⋅ day(-1)) with its limits of agreement ranging from -103.3 to 177.1 minutes ⋅ day(-1). CONCLUSION: The multisensory monitor is capable of accurately measuring sedentary activities and distinguishing them from light-intensity activities. Compared to the multisensory monitor, our results showed that AL provides valid estimate of overall sedentary time.

Prefrontal cortex oxygenation during incremental exercise in chronic fatigue syndrome.

This study examined the effects of maximal incremental exercise on cerebral oxygenation in chronic fatigue syndrome (CFS) subjects. Furthermore, we tested the hypothesis that CFS subjects have a reduced oxygen delivery to the brain during exercise. Six female CFS and eight control (CON) subjects (similar in height, weight, body mass index and physical activity level) performed an incremental cycle ergometer test to exhaustion, while changes in cerebral oxy-haemoglobin (HbO2), deoxy-haemoglobin (HHb), total blood volume (tHb = HbO2 + HHb) and O2 saturation [tissue oxygenation index (TOI), %)] was monitored in the left prefrontal lobe using a near-infrared spectrophotometer. Heart rate (HR) and rating of perceived exertion (RPE) were recorded at each workload throughout the test. Predicted VO2peak in CFS (1331 +/- 377 ml) subjects was significantly (P < or = 0.05) lower than the CON group (1990 +/- 332 ml), and CFS subjects achieved volitional exhaustion significantly faster (CFS: 351 +/- 224 s; CON: 715 +/- 176 s) at a lower power output (CFS: 100 +/- 39 W; CON: 163 +/- 34 W). CFS subjects also exhibited a significantly lower maximum HR (CFS: 154 +/- 13 bpm; CON: 186 +/- 11 bpm) and consistently reported a higher RPE at the same absolute workload when compared with CON subjects. Prefrontal cortex HbO2, HHb and tHb were significantly lower at maximal exercise in CFS versus CON, as was TOI during exercise and recovery. The CFS subjects exhibited significant exercise intolerance and reduced prefrontal oxygenation and tHb response when compared with CON subjects. These data suggest that the altered cerebral oxygenation and blood volume may contribute to the reduced exercise load in CFS, and supports the contention that CFS, in part, is mediated centrally.