Both PPG and heart-rate sensors provide an acceptable agreement for the measurement of rMSSD when compared with ECG. Smartphone PPG technology may be a preferred method of HRV data collection for athletes due to its practicality and ease of use in the field.

Objectives: Ingested ketogenic agents offer the potential to enhance endurance performance via the provision of an alternative exogenous, metabolically efficient, glycogen-sparing fuel (i.e. ketone bodies). This study aimed to assess the impact of combined carbohydrate and 1,3-butanediol (CHO-BD) supplementation on endurance performance, blood beta-hydroxybutyrate (βHB) concentration and glycolytic activity, in comparison to carbohydrate supplementation alone (CHO). Design: Eleven male runners (age 38 ± 12 years, mass 67.3 ± 6.5 kg, height 174.5 ± 5.0 cm, V O2peak 64.2 ± 5.0 ml•kg-1 •min-1) performed two experimental trials in a randomised crossover design. Methods: Each trial consisted of 60 min of submaximal running, followed by a 5 km running time-trial (TT), and was performed following the ingestion of an energy matched ~650 ml drink (CHO-BD or CHO). Results: There was no difference in TT completion time between the trials (CHO: 1265 ± 93, CHO-BD: 1261 ± 96 s; p=0.723). However, blood βHB concentration in the CHO-BD trial was at least double that of the CHO trial at all time points following supplementation (p<0.05). While blood lactate concentration was lower in the CHO-BD versus CHO trial after 30 min submaximal exercise (CHO-BD: 1.46 ± 0.67 mmol•L-1 , CHO: 1.77 ± 0.46 mmol•L-1 , p=0.040), it was similar at other time points. Blood glucose concentrations were higher post-TT in the CHO-BD trial (CHO-BD: 5.83 ± 1.02 mmol•L-1 , CHO: 5.26 ± 0.95 mmol•L-1 , p=0.015). Conclusions: An energy matched CHO-BD supplementation drink raised βHB concentration and acutely lowered blood lactate concentration, without enhancing 5km TT running performance.

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Purpose: The validity of the critical speed (CS) concept has been investigated in front crawl swimmers using protocols involving multiple performance trials. The reliability and practical feasibility of CS protocols with strong face validity remain unknown in all four swimming strokes. This study aimed to assess reliability and practical feasibility of a widely used CS protocol in all four strokes. Methods: 32 national-level swimmers (butterfly n=7, 19 ± 2 years old; backstroke n=8, 18 ± 2 years old; breaststroke n=7, 18 ± 2 years old; front crawl n=10, 17 ± 2 years old) performed three 200-m and three 400-m performance trials in their specialist stroke over a three-week period. CS and supra-CS distance capacity (D’) were modelled from the linear relationship between distance and time. At the end of the three weeks, all swimmers were asked whether they felt they could or would want to complete an 800-m performance trial as part of a CS protocol. Results: CS derived from 200-m and 400-m performance trials is reliable (typical error ≤ 0.04 m.s-1; coefficient of variation < 4% for all strokes) while D’ is not (typical error between 4 to 9 m; coefficient of variation 13-45%) . Response rate to the follow-up questions was 100%. Only a few butterfly swimmers would want to (14%) or felt they could (29%) complete an 800-m performance trial with more positive responses for breaststroke (57% and 71%), backstroke (75% and 100%), and front crawl swimmers (90% and 100%).Conclusion: Using 200-m and 400-m performance trials is a reliable and practical method for determining CS in backstroke, breaststroke and front crawl swimmers. Including an 800-m performance trial would not be practical with butterfly swimmers, would be challenging with breaststroke swimmers, but would be feasible with front crawl and backstroke swimmers.