Running performance under fatigue: risks and learnings
You start a race full of energy and optimism, but in the last few kilometers your body feels heavier and your legs can’t keep up the pace you want. Fatigue affects our running gait (kinematics), which can eventually lead to an increased risk of injury. In this article, we discuss the findings of the Run3D study on the risks of fatigue in running and how best to manage it.
Running speed
As you become more fatigued, your running speed decreases. Your running speed is determined by your cadence (the number of steps you take per minute) and your stride length (how long your steps are). As fatigue sets in, you start to take fewer and shorter steps: both your cadence and stride length decrease. Fatigue also changes your running gait; you may lean forward more with your upper body, not fully extend your knee upon foot strike (increased knee flexion), and have reduced hip and knee movement. Experts believe these are built-in mechanisms in our bodies to conserve energy and protect us from injuries.
When stride length decreases without an increase in cadence, running speed decreases. To understand what else changes in the gait when a runner is fatigued, Run3D conducted an experiment using their own technology. Various runners were asked to test the effects of running under fatigue using the Run3D gait analysis. A baseline measurement was taken before the runners completed a half marathon, followed by another 3D analysis post-race. For both analyses, runners were asked to run at the same pace to identify changes when running speed remained constant. Significant changes highlighted the effects of fatigue on gait:
- Increased cadence: the number of steps per minute is higher than normal.
- Increased knee flexion: the knee bends more upon foot strike.
- Reduced stride length: steps are shorter than normal.
- Reduced stance time: the foot stays on the ground for a shorter period during running.
What happens in your body?
As fatigue sets in, our ability to maintain trained movement patterns is affected, and our body adjusts to conserve energy. While this tactic helps us reach the finish line, it increases our injury risk and decreases our running speed. The above-described study shows that the risk factors in the gait identified before the race were more pronounced after the race when the participant was fatigued. The following factors affect running speed and/or increase the risk of injury:
- Increased hip internal rotation: the hip rotates more inward than usual.
- Increased hip adduction: the hip moves more inward than usual.
- Increased knee internal rotation: the knee rotates more inward than usual.
- Increased rearfoot eversion: the heel of the foot tilts outward more than usual.
- Reduced cadence: the number of steps per minute is lower than normal.
- Increased trunk rotation: the upper body rotates more during running than normal.
- Reduced knee flexion at foot strike and during stance phase: the knee bends less when the foot hits the ground and while standing on that leg.
A 2018 study using 3D analysis also confirms that more experienced runners experience less significant changes in their movement patterns when fatigued compared to less experienced runners. Novice runners mainly struggled with increased forward trunk lean, increased ankle flexion, and reduced knee flexion.
What can we conclude from this?
To date, there are no specific solutions to counteract fatigue and its effects on running performance. However, there are several things you can do:
- Gain experience: Ensure you train properly for your running goals.
- Measure stride length and cadence: Speed = stride length x cadence. The Run3D study shows that as fatigue takes over, stride length decreases. During training, focus on increasing your cadence to try to maintain your speed towards the end of a race.
- Gait analysis and strength training: Measurement is key! Run3D gait analysis can provide insights into the risks within your gait. Knowing where the risks are allows you to address them in your training to prevent pain and injuries.
Run3D
A Run3D-gait analysis creates a 3D model of your running gait. We can see where your weak and strong points (risk and performance markers) are. This information is summarized in a Run3D Performance Report. Based on the risk and performance markers from your report, you will work with one of our specialists on the track. Here you will receive cues to implement changes in your gait. By changing your gait based on your unique results, you prevent injuries and achieve your best time ever!
Schedule your Run3D appointment here and fly across the finish line!