Jerk - An Underutilized Measurement Of Movement Efficiency
In this article we'll explore how jerk, the rate that acceleration changes, can be used to identify changes in movement efficiency .
In a previous article titled, A Lab In Your Pocket - The Future Of High Performance, I explained how unlike first-generation muscle oximeters, such as the Moxy Monitor, BSX Insight, and Humon Hex, NNOXX collects a range of biomarkers in real time, providing a comprehensive view of your performance. In this article i’m going to expand on these ideas, discussing how NNOXX’s ability to measure jerk can help coaches and athletes better understand their bodies response to exercise.
⦿ Jerk - An Underutilized Measurement Of Movement Efficiency
Recently, I've been interested in exploring how we can extract additional meaningful data from NNOXX's measurements. This led me to look at the relationship between jerk and fatigue. Whereas acceleration represents the rate at which velocity changes over time, jerk represents the rate at which acceleration changes. Thus, jerk captures the smoothness of a motion and can be used to quantify movement efficiency.
What's most interesting about jerk is that it's generally uncorrelated with power output, velocity, and acceleration during exercise. Additionally, if an athlete's movement patterns are smooth and efficient, jerk will remain stable even as their speed or power increases.
However, if an athlete's movement efficiency decreases as power increases or if their biomechanics start to compensate, the jerk will increase. This is common in high-fatigue conditions.
In the image above, an athlete's muscle oxygenation (SmO2) and jerk are displayed as time-series measurements during a workout composed of.... 5-minute Echo Bike @400w watts x4 sets, resting 1-minute between.
Notice that with each set, the change in SmO2 from rest to the end of the interval increases, indicating that this load (400 watts) is imposing more and more stress on each set as the athlete fatigues. Notably, we can also see their jerk increasing across these sets, telling us that their movement efficiency worsens as they fatigue. Knowing this, we can potentially use jerk as a real-time indicator of movement efficiency, allowing us to alter an athlete's training as they fatigue to reduce their risk of injury or better enhance performance outcomes.
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