Algorithms for using an activity-based accelerometer for identification of infant sleep-wake states during nap studies.

OBJECTIVE: To determine the accuracy of using different algorithms on the output from an Actical accelerometer, a device normally used to measure physical activity, to distinguish sleep from wake states. METHODS: Thirty-one infants aged 10-22 weeks wore the accelerometer on the shin for a daytime nap recording in tandem with polysomnography. Sleep-wake epochs were identified using four computations/algorithms: the zero-threshold computation, two common algorithms used for wrist-based devices (Sadeh and Cole), and a new algorithm developed for this study (count-scaled). Accuracy was examined in direct epoch comparison with polysomnography using 15-, 30- and 60-s sampling epochs. RESULTS: Overall agreements (accuracy) for sleep-wake states were >80% for all computations. The count-scaled algorithm sampling 15-s epochs gave the highest accuracy, with sensitivity (sleep agreement) at 86% and specificity (awake agreement) at 85%. Other computations yielded higher sensitivity at the expense of specificity. Another way to assess the accuracy of identification of sleep-wake states was to compare sleep parameter outputs. All computations and sampling epochs were significantly correlated with total sleep time (r=0.76-0.88), sleep latency (r=0.70-0.93), sleep efficiency (r=0.76-0.87), and wake time after sleep onset (r=0.41-0.53). The number of awakenings after sleep onset was overestimated by accelerometry. CONCLUSIONS: The Actical accelerometer, designed to measure physical activity, can reliably identify sleep in infants during napping, with the count-scaled algorithm showing some advantages over other methods for accurate identification of sleep-wake epochs.

Effects of prior heavy exercise on energy supply and 4000-m cycling performance.

PURPOSE: This study was designed to determine the effects of prior exercise on energy supply and performance in a laboratory-based 4000-m time trial. METHODS: After one familiarization trial, eight well-trained cyclists (mean +/- SD; age = 30 +/- 8 yr, body mass = 78.7 +/- 8.6 kg, stature = 181 +/- 5 cm, .VO2 peak = 63.7 +/- 6.7 mL.kg.(-1)min(-1), peak power output (PPO) = 366 +/- 39 W) performed three 4000-m laboratory-based cycling time trials each preceded by one of three prior exercise regimens in randomized order: no prior exercise (control), prior heavy exercise, and self-selected prior exercise. RESULTS: Cyclists adopted a wide range of self-selected prior exercise regimens: duration ranged = 11-80 min, intensity = 48-120% PPO, and recovery = 2-11 min. Relative to control, pre-time-trial blood lactate was raised by 2.5 +/- 1.9 and 1.4 +/- 1.5 mmol.L(-1) after prior heavy and self-selected exercise, respectively. The 4000 m was completed 2.0 +/- 2.3% and 2.2 +/- 1.9% faster after prior heavy and self-selected exercise regimens, respectively, and mean power output was 5.4 +/- 3.6% and 6.0 +/- 5.8% higher, respectively. The overall aerobic contribution (.VO2) and oxygen deficit were not different between conditions (approximately 323 +/- 23 and approximately 64 +/- 22 mL.kg,(-1) respectively), although .VO2 was higher (P < 0.05) in the prior heavy (by 2.1-5.8 mL.kg(-1).min(-1)) and self-selected (2.5-4.3 mL.kg(-1).min(-1)) regimens compared with the control throughout the first half of the time trial. CONCLUSION: Very high intensity cycling performance was improved after both self-selected and prior heavy exercise. Such priming increased the early aerobic contribution but did not change overall aerobic contribution or oxygen deficit. Thus, athletes seem to manage their energy potential to exploit the available anaerobic capacity, independent of the aerobic contribution. Athletes are advised to perform a bout of heavy exercise as part of their prior exercise regimen.