Preprint / Version 1

Overreached endurance athletes demonstrate alterations in exercising carbohydrate utilization applicable to training monitoring




Overtraining, continuous glucose monitoring, low energy availability, resting metabolic rate, cycling


Purpose: To investigate whether carbohydrate utilization is altered during exercise in overreached endurance athletes, and to examine the utility of continuous glucose monitors (CGM) to detect overreaching status. Methods: Eleven endurance athletes (M:8, F:3) completed a 5-week training block consisting of 1-week of reduced training (PRE), 3-weeks of high-intensity overload training (POST), and 1-week of recovery training (REC). Participants completed a Lamberts and Lambert Submaximal Cycling Test (LSCT) and 5km time-trial at PRE, POST, and REC timepoints, 15min following the ingestion of a 50g glucose beverage with glucose recorded each minute via CGM. Results: Performance in the 5km time-trial was reduced at POST (∆-7±10W, P=0.04, ηp2=0.35) and improved at REC (∆12±9W from PRE, P=0.01, ηp2=0.66), with reductions in peak lactate (∆-3.0±2.0mmol/L, P=0.001, ηp2=0.71), peak HR (∆-6±3bpm, P<0.001, ηp2=0.86), and Hooper-Mackinnon well-being scores (∆10±5a.u., P<0.001, ηp2=0.79), indicating athletes were functionally-overreached. The respiratory exchange ratio was suppressed at POST relative to REC during the 60% (POST: 0.80±0.05, REC: 0.87±0.05, P<0.001, ηp2 =0.74), and 80% (POST:0.93±0.05, REC: 1.00±0.05, P=0.003, ηp2 =0.68) of HR-matched submaximal stages of the LSCT. CGM glucose was reduced during HR-matched submaximal exercise in the LSCT at POST (P=0.047, ηp2 =0.36), but not the 5km time-trial (P = 0.07, ηp2 =0.28) in overreached athletes. Conclusion: This preliminary investigation demonstrates a reduction in blood glucose and carbohydrate oxidation during submaximal exercise in overreached athletes. The use of CGM during submaximal exercise following standardised nutrition could be employed as a monitoring tool to detect overreaching in endurance athletes.


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