The Impact of Intense Training on Heart Rate Variability & Body Composition in Cyclists
Jul 20, 2023Today, we examine how intensified training periods affect resting metabolic rate (RMR), body composition and performance in trained endurance athletes.
Periods of functional overreaching are deliberately programmed to amplify training adaptations. However, the athlete must balance stimulus and fatigue appropriately. If imbalances occur over long periods, the debilitating state of overtraining can develop.
Woods et al. (2018) recruited 13 cyclists to complete a six-week training programme to elicit overreaching and measured their physiological and psychological responses:
Week 1: Normal = Regular training load (TL).
Week 2: Build = 120% TL.
Weeks 3 & 4: Loading = 140%, 150% TL.
Weeks 5 & 6: Recovery = 80% TL.
The intensified training block significantly decreased RMR, body mass, fat mass and heart rate variability (HRV). The cyclists also experienced decreased aerobic and anaerobic performance and increased mood disturbances.
The authors state that RMR reductions were most likely a result of sub-optimal energy intake and low energy availability, which can occur during periods of heavy training when energy intake doesn’t meet energy output. A reduction in appetite perhaps drove this during harder training weeks.
A reduction in RMR may also be linked with poorer HRV scores and changes in thyroid activity: i.e. energy conservation.
On average RMR reductions were approx. 29kcal to 26kcal/kg of fat-free mass per day: A 75kg cyclist with 15% body fat equates to an RMR change from 1848 to 1657kcal per day.
A relationship was found between mood disturbances, RPE and HRV. Interestingly, these feedback markers were the earliest to change and may be a reliable and easy way to monitor fatigue.
The observed changes are most likely the body’s attempt to conserve energy when insufficient calories are consumed. Notably, these measurements returned to baseline following a two-week recovery period (most likely when sufficient energy was consumed).
Therefore, to reduce the likeliness of these unfavourable adaptations, ensure you fuel the ride!
- Coach Chris
If you're a road, mountain bike, gravel or track cyclist and want to take your performance and physique to the next level...let the FTR coaches show you exactly how to achieve this inside the Fuel The Ride Academy.
