Let’s explore how mechanical power can serve as a more accurate indicator of neuromuscular load in rugby.
Quantifying mechanical load — the neuromuscular and musculo-tendinous stress experienced by players during training and competition — is essential for effective load management, injury prevention, and performance optimisation in team sports such as rugby.
But how many actions truly qualify as high-intensity mechanical loads? And how accurately can we identify them? The answer depends on the methods used to measure them.
Traditionally, mechanical load has been estimated by quantifying high-speed running and counting the number of accelerations above a fixed threshold (commonly set at 2.5 or 3 m/s²). While simple and widely adopted, this method treats speed and acceleration as independent variables and relies on absolute thresholds. As a result, it can sometimes fail to capture truly high-intensity efforts.
At the recent ECSS Congress in Rimini, Alberto Botter and colleagues shared new insights suggesting that external mechanical power provides a more comprehensive and sensitive metric for measuring neuromuscular load in professional rugby. This approach may help overcome some of the key limitations of traditional monitoring methods.
Acceleration alone misses the point
To illustrate the problem, consider the following scenario: a player performs four maximal sprints, all of which reach the same top speed. Two of them start from a standstill or low speed (0 and 6 km/h), while the other two begin from higher velocities (12 and 22 km/h).
According to traditional acceleration-based metrics, only the first two sprints are classified as “high-intensity”, simply because they exceed the fixed threshold of 2.5 m/s². The other two go undetected, not because they are less demanding, but because starting from a higher speed naturally results in lower peak acceleration.
This highlights a fundamental flaw: acceleration alone doesn’t reflect the true mechanical demands of movement. Acceleration is strongly affected by starting speed, while the intensity depends on the interaction between speed and acceleration. Treating them as isolated variables leads to a misrepresentation of the mechanical loads.
From Acceleration to Mechanical Power
To overcome this limitation, a new approach based on mechanical power has been introduced. This method combines both speed and acceleration into a single, physics-derived metric that better reflects the real demands placed on the athlete.
How it works:
- each athlete has a unique Acceleration–Speed Profile (ASP), a straight-line relationship that describes their maximum acceleration capacity across different running speeds. It defines the upper limit of acceleration they can generate at any given velocity.
- Using the ASP, we can calculate external mechanical power — the amount of mechanical work done per unit time during sprinting. It’s determined by: Power = Horizontal Force × Instantaneous Velocity.
This metric provides a continuous and individualised measure of neuromuscular load.
Identifying high-intensity efforts: the power of “bursts”
A key advantage of using mechanical power is the ability to detect what we call bursts — short, high-intensity efforts where the athlete’s external mechanical power exceeds 80% of their individual maximum.
With this method, all four sprints — regardless of their starting velocity — are correctly identified as high-intensity efforts, because they each exceed the 80% power threshold.
In contrast, only two of them would be flagged by traditional acceleration metrics, which rely on an arbitrary fixed threshold (e.g., 2.5 m/s²). As a result, two demanding efforts go completely undetected, simply because they start at higher speeds where peak acceleration is lower.
This leads to a systematic underrepresentation of truly demanding actions.
Why does it matter?
- No blind spot: unlike fixed threshold zones, mechanical power provides a full-spectrum view of sprint load — even when acceleration alone wouldn’t flag the effort.
- Individualisation: each athlete’s ASP and resulting power curve are unique, making the metric highly specific to their capabilities and sprint mechanics.
Ultimately, by integrating acceleration and velocity into a single, physics-based metric, mechanical power provides a more accurate, personalised, and actionable way to monitor neuromuscular load — both in training and in competition.
Rugby vs football: same metric, different story
When applying this power-based approach to real match data, the differences between sports became clear.
Botter and colleagues analysed over 1,100 player observations from 51 official rugby matches, comparing the number of high-intensity efforts detected by traditional acceleration thresholds and by the mechanical power method.
Here’s what they found:
- In rugby, the average bursts-to-accelerations ratio was 0.43, meaning that nearly half of the actions above 2.5 m/s² didn’t actually qualify as high-intensity when measured against the ASP method.
- In football, the ratio was 1.59, suggesting the opposite: many actions that were not flagged by acceleration thresholds did exceed the 80% power threshold and should be considered high-intensity efforts.
These contrasting results highlight how the traditional method tends to misrepresent high-intensity efforts across sports — overestimating them in rugby and underestimating them in football.
Such differences are likely rooted in the distinct movement patterns characteristic of each sport. In rugby, high-intensity actions often begin from a standstill or low-speed context. This condition is less common in football, where players typically initiate maximal efforts from a jogging pace rather than from a complete stop.
Why it matters for performance analysis
These findings emphasise the need to move beyond conventional acceleration-based metrics for evaluating mechanical load in team sports. The mechanical power approach, by integrating acceleration and velocity into a single, individualised parameter derived from each athlete’s Acceleration–Speed Profile, provides a more valid and sensitive indicator of neuromuscular load. Not only does it better capture high-intensity efforts across different movement contexts, but it also highlights sport-specific differences — as seen in rugby and football — that are crucial for tailored load monitoring and performance optimisation. Embracing this method could significantly enhance the way practitioners evaluate and manage physical demands in elite sport.
Author: Alberto Botter
For more details, see the study presented at the ECSS Congress in Rimini by Botter et al., and related research on mechanical power analysis in team sports.
References
1 – “Mechanical and metabolic power in accelerated running—PART I: the 100-m dash”, di Prampero PE et al., European Journal of Applied Physiology, 2023. DOI: 10.1007/s00421-023-05236-x.
2 – “Energy cost of running uphill as compared to running on the level with impeding horizontal forces”, Osgnach C et al., European Journal of Applied Physiology; volume 125, pp. 61–69; 2024. DOI: 10.1007/s00421-024-05587-z.