Measuring Activity Energy Expenditure: Accuracy of the GT3X+ and Actiheart Monitors

International Journal of Exercise Science 6(3) : 217-229, 2013. The purpose was to determine the accuracy of the GT3X+ and Actiheart monitors for estimating energy expenditure (EE) and steps. Additionally, to investigate agreement between waist- and wrist-mounted GT3X+ EE outputs. Nineteen participants (mean age=30) completed three treadmill walking trials at self-selected slow, medium, and fast speeds while wearing two GT3X+ (waist and wrist) and an Actiheart. Activity monitor EE was compared to indirect calorimetry criterion EE using Pearson correlations and ANOVAs. A Bland-Altman plot was used to investigate agreement between GT3X+ waist- and wrist-determined EE. GT3X+ determined steps were compared to researcher-counted steps using ANOVAs. EE estimates from all monitors correlated highly with the criterion (r ranged from .72 to .82). However, the GT3X+ (waist and wrist) underestimated EE during slow walking and overestimated EE during fast walking. There were no differences among GT3X+ (waist and wrist) estimates of EE and the criterion during the medium trial. Actiheart estimated EE was not significantly different from measured EE during all trials. The Bland-Altman plot indicated that at EE rates above 4 kcal·min-1, the GT3X+ worn on the wrist underestimated EE compared to when it was worn on the waist. There were no differences between GT3X+ waist-determined steps and researcher-counted steps for all trials. GT3X+ EE correlates highly with measured EE, but has poor absolute agreement during slow and fast walking. GT3X+ step estimates are accurate across the continuum of walking speeds when waist (but not wrist) mounted. Wrist-mounted device outputs are not comparable to waist-mounted outputs. The Actiheart accurately estimates EE

Mass and Energy Balance Estimation of Yala Glacier (2011–2017), Langtang Valley, Nepal

Six-year glaciological mass balance measurements, conducted at the Yala Glacier between November 2011 and November 2017 are presented and analyzed. A physically-based surface energy balance model is used to simulate summer mass and energy balance of the Yala Glacier for the 2012⁻2014 period. Cumulative mass balance of the Yala Glacier for the 2011⁻2017 period was negative at −4.88 m w.e. The mean annual glacier-wide mass balance was −0.81 ± 0.27 m w.e. with a standard deviation of ±0.48 m w.e. The modelled mass balance values agreed well with observations. Modelling showed that net radiation was the primary energy source for the melting of the glacier followed by sensible heat and heat conduction fluxes. Sensitivity of mass balance to changes in temperature, precipitation, relative humidity, surface albedo and snow density were examined. Mass balance was found to be most sensitive to changes in temperature and precipitation