Why GPS systems may be miscalculating your athlete’s mechanical load – Part 2

By April 4, 2019 December 6th, 2019 News

If you’re trying to track mechanical load, GPS systems won’t give you the whole picture

This article is a follow up to Why GPS systems may be miscalculating your athlete’s mechanical load – Part 1

Training aims to induce physical adaptations for enhanced performance whilst reducing the risk of injury. However to increase endurance, speed, strength and/or power, a sufficient training stimulus is needed. But an excessive training load can put an individual at risk of injury. To prescribe adequate training loads for the desired adaptations, it is critical to have a thorough understanding of the relationship between the loads experienced by the body and the physical adaptations. GPS systems do not analyze this. Therefore, the physiological and biomechanical load-adaptation pathways could be evaluated separately [1]

“Historically, biomechanical loads have been poorly quantified in the field and are thus not well understood. Companies like IMeasureU, now part of Vicon, are bridging the gap between the lab and the field and enabling investigations that accurately quantify biomechanical loads”

GPS Limitations

Physiological loads can be defined as the biochemical stresses experienced by the cardiovascular system. Enough stimuli may lead to desired adaptations such as increased metabolic and/or cardiac efficiency, while an over or under load could cause energy depletion or cardiac atrophy. Examples of commonly used measures to assess the internal physiological loads include oxygen uptake (VO2), heart rate, blood lactate and/or self-reported ratings of perceived exertion (RPE). The external physiological loads, on the other hand, are commonly quantified by GPS-derived metrics such as the total distance covered or time at certain speed or acceleration thresholds. Although these variables may be used to quantify and evaluate the aerobic and metabolic demands of training, they do not describe the loads experienced by the musculoskeletal system [2].

Advances in Technology

Biomechanical loads can be defined as the forces and stresses (i.e. normalized, distributed force) acting on the various hard and soft tissues (e.g. muscles, tendons, bones, cartilage) of the body. The repetitive mechanical loading of subsequent training sessions causes tissue-damage, which is necessary for positive adaptations such as stiffer tendons or muscle hypertrophy. However, an accumulation of damage over time can progressively weaken the tissues and ultimately lead to failure of a particular structure (i.e. overuse injuries) [3]. In contrast to the physiological loads, the biomechanical demands of training have been historically difficult to measure in the field. This limits detailed descriptions of the biomechanical load-adaptation pathways. However, recent advances in technology such as small, synchronized inertial sensors are enabling scientists, practitioners, and coaches to accurately measure, and therefore manage, biomechanical load in the field. Scientists, once previously constrained to the lab, can now work alongside practitioners, coaches and athletes to measure, analyze, and action field-based insights. Performance, return to play programming and injury risk reduction can then be improved with this data. The tech is here but up until now, what’s been missing is aligning sensors, software, and science. We now have a way to directly link sensor data to known underlying biomechanical models, and then present it in a simple, actionable way to practitioners, coaches, and athletes.

What Does the Research Say?

Much research has focused on measuring external or whole-body biomechanical loads. Different measures derived from a single, center of mass, body-worn accelerometer have been used to assess whole-body training load. However, a biomechanical underpinning of these metrics has been lacking, which has made their use for biomechanical load monitoring questionable. These single accelerometers have also been used to estimate ground reaction forces (GRFs) as a measure of external biomechanical load. Several studies have shown though that using individual accelerometers might not be able to estimate GRF across different sports movements [4,5]. Furthermore, the GRF is not reflective of the way the human body attenuates load, so one should be cautious when using individual accelerometers or GRFderived load measures as an accurate measure of whole-body biomechanical loading [6].

Field-based Internal Loading Assessment

Injuries are known to ultimately be the result of mechanical stresses that overcome the strength of a given tissue [3]. To gain a more in-depth understanding of injuries, whether overuse or acute, accurate quantification of the internal biomechanical force is thus required. Joint moments can be calculated using modeling techniques to gain insight into the muscle-tendon and joint contact forces. Tibial accelerations have also been used as a surrogate measure of impact force experienced by the bone. Despite previous success in quantifying these forces in laboratory environments, either through direct measurements or advanced musculoskeletal modeling techniques, field-based measurements of internal loads have been unavailable until recently. IMeasureU’s IMU Step solution has solved this challenge by combining sensors, software, and science to monitor biomechanical lower limb load.
Why-GPS-systems-may-be-miscalculating your-athlete's-mechanical-load-outline-athlete-running

Conclusion

Ecologically valid monitoring of training load is essential for real-world performance enhancement and injury prevention, but an accurate understanding of both the physiological and biomechanical load-adaptation pathways is required [1]. Historically, biomechanical loads have been poorly quantified in the field and are thus not well understood. Companies like IMeasureU, now part of Vicon, are bridging the gap between the lab and the field and enabling investigations that accurately quantify biomechanical loads.

Interested in how IMU Step can help you quantify mechanical load and remove the guesswork from your own RTP protocols? Click here to learn more.

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