ObjectivesThe aims of this study were to: (1) determine the validity and reliability of the Nova Biomedical Lactate Plus portable analyzer, and quantify any fixed or proportional bias; (2) determine the effect of any bias on the determination of the lactate threshold and (3) determine the effect that blood sampling methods have on validity and reliability.DesignIn this method comparison study we compared blood lactate concentration measured using the Lactate Plus portable analyzer to lactate concentration measured by a reference analyzer, the YSI 2300.SettingUniversity campus in the USA.ParticipantsFifteen active men and women performed a discontinuous graded exercise test to volitional exhaustion on a motorised treadmill. Blood samples were taken via finger prick and collected in microcapillary tubes for analysis by the reference instrument at the end of each stage. Duplicate samples for the portable analyzer were either taken directly from the finger or from the micro capillary tubes.Primary outcome measurementsOrdinary least products regressions were used to assess validity, reliability and bias in the portable analyzer. Lactate threshold was determined by visual inspection.ResultsThough measurements from both instruments were correlated (r=0.91), the differences between instruments had large variability (SD=1.45 mM/l) when blood was sampled directly from finger. This variability was reduced by ∼95% when both instruments measured blood collected in the capillary tubes. As the proportional and fixed bias between instruments was small, there was no difference in estimates of the lactate threshold between instruments. Reliability for the portable instrument was strong (r=0.99, p<0.05) with no proportional bias (slope=1.02) and small fixed bias (−0.19 mM/l).ConclusionsThe Lactate Plus analyzer provides accurate and reproducible measurements of blood lactate concentration that can be used to estimate workloads corresponding to blood lactate transitions or any absolute lactate concentrations.

Physical activity benefits for disease prevention are well-established. Smartphones offer a convenient platform for community-based step count estimation to monitor and encourage physical activity. Accuracy is dependent on hardware-software platforms, creating a recurring challenge for validation, but the Apple iPhone® M7 motion co-processor provides a standardised method that helps address this issue. Validity of the M7 to record step count for level-ground, able-bodied walking at three self-selected speeds, and agreement with the StepWatch was assessed. Steps were measured concurrently with the iPhone® (custom application to extract step count), StepWatch and manual count. Agreement between iPhone® and manual/StepWatch count was estimated through Pearson correlation and Bland-Altman analyses. Data from 20 participants suggested that iPhone® step count correlations with manual and StepWatch were strong for customary (1.3 ± 0.1 m/s) and fast (1.8 ± 0.2 m/s) speeds, but weak for the slow (1.0 ± 0.1 m/s) speed. Mean absolute error (manual-iPhone®) was 21%, 8% and 4% for the slow, customary and fast speeds, respectively. The M7 accurately records step count during customary and fast walking speeds, but is prone to considerable inaccuracies at slow speeds which has important implications for certain patient groups. The iPhone® may be a suitable alternative to the StepWatch for only faster walking speeds.

As an appealing alternative to reference glucose analyzers, portable glucometers are recommended for self-monitoring at home, in the field, and in research settings. The purpose was to characterize the accuracy and precision, and bias of glucometers in biomedical research. Fifteen young (20-36 years; mean = 24.5), moderately to highly active men (n = 10) and women (n = 5), defined by exercising 2 to 3 times a week for the past 6 months, were given an oral glucose tolerance test (OGTT) after an overnight fast. Participants ingested 50, 75, or 150 grams of glucose over a 5-minute period. The glucometer was compared to a reference instrument. The glucometer had 39% of values within 15% of measurements made using the reference instrument ranging from 45.05 to 169.37 mg/dl. There was both a proportional (-0.45 to -0.39) and small fixed (5.06 and 0.90 mg/dl) bias. Results of the present study suggest that the glucometer provided poor validity and reliability results compared to the results provided by the reference laboratory analyzer. The portable glucometers should be used for patient management, but not for diagnosis, treatment, or research purposes.