The Impact of Fatigue on Endurance Performance
by Doug Stewart
Durability, fatigability, fatigue resistance, or as it used to be called, stamina, refer to one’s ability to sustain prolonged endurance exercise. However, although we know that over time performance drops, what is causing this, and why are some athletes more durable than others?
A recently published paper explored this by taking 14 cyclists (1 female) with an average VO2Max of 59.9 and 34 years of age. The participants undertook two tests. The first involved a ramp test to determine thresholds. The second one, 7 days apart, involved a ramp test, followed by 2 hours of cycling at a moderate intensity (determined by the initial test 7 days earlier), and then a repeat of the ramp test (after the 2 hours of moderate cycling).
Essentially, the sport scientists were investigating the impact that 2 hours of cycling had on power output and physiological measures, such as heart rate.
They discovered that the power output significantly decreased after the 2 hours of cycling. This loss of power was attributed to reduced cycling efficiency and higher heart rates.
Source: Stevenson et al., 2022
Although heart rate did rise overall, it can be seen that 3 of the riders had lower readings, but all of them produced less power. So clearly there are individual variances in how individuals responded to the 2 hours of cycling.
For three of them their heart rate dropped in line with power output dropping, whilst for the majoirty heart rate rose whilst power was lower.
During the 2 hours of cycling the participants’ heart rates rose throughout as a general trend:
Source: Stevenson et al., 2022
This increase may be down to dehydration, higher core temperature and the added metabolic demand when cycling at the fixed power output. Moreover, with this drift, it may in part explain why the heart rate was higher (as per the earlier graph) between the pre- and post-test readings – and likely contributed to the power output being lower after the two hours of cycling.
When assessing durability, it is important that each athlete is analysed individually, as cardiac drift may differ for each of us. Furthermore, if looking to improve durability, working to ensure lower cardiac drift may help an athlete have energy at the end of a workout to produce the same output at the same intensity as they are capable of at the start, or at the very least minimise the drop.
References:
Stevenson, J.D., Kilding, A.E., Plews, D.J. and Maunder, E., 2022. Prolonged cycling reduces power output at the moderate-to-heavy intensity transition. European journal of applied physiology, pp.1-10.