KINEMATIC CHANGES IN PLAYER LOAD? SYSTEMS INTERROGATION

ABSTRACT

The purpose of this paper is to evaluate the use and utility of Sense3, a sensor system embedded in compression shorts that measure kinematic changes, muscle activation and physiology in elite athletes.

THE PROBLEM

Elite sports teams have been monitoring athlete loads through wearable technology for close to 10 years, yet most leagues and teams have yet to see a quantifiable reduction in athlete injury or a significant change in performance-based outputs. In many cases, the technologies provide a singular load metric “score” indicating a difference from game to game- or practice sessions. Practitioners are left to make “inferences” on why the score changed, without forming a direct rationale as to which biological system may be in deficit or a cause.

While some practitioners add layers of technology, the interface between systems, noise to signal coefficient (quality) of the data, and repeatability of use due to form factor and utility complexities all present challenges to determine actual cause and effect relationships.

The introduction of Sense3 compression garment by Strive is being reviewed as a potential breakthrough in data aggregation and athlete management for elite teams globally.

BACKGROUND

Athlete load monitoring has become an “in-vogue” discussion over the last five years in elite team sports, primarily since the introduction of GPS monitoring. Over 5,000 teams globally use GPS monitoring to identify load trends in athletes (1), for the universal purpose of understanding (a) which athletes may be at risk of injury and to identify (b) the training processes that lead to peak performance outcomes.

Elite sport practitioners (Sports Science and Performance Coaches) aggregate load measures and when performance issues are identified, they begin to infer reasons why a change is happening. In many cases practitioners defer to secondary and tertiary assessments to identify a biological systems variance. In an attempt to simplify this process, some technologies use linear calculations. Most models, however, are fraught with error (and in some cases, philosophical debate). Estimated Metabolic Power from GPS monitoring is one example that has created controversy among many elite sports practitioners. (2)

FATIGUE

In humans, muscle fatigue can be defined as an exercise-induced decrease in the ability to produce force. (3) Individual muscle fatigue is defined as a decrease in maximal force or power production in response to contractile activity. (4) It can originate at different levels of the motor pathway and is usually divided into central and peripheral components. Peripheral fatigue is produced by changes at or distal to the neuromuscular junction. Central fatigue originates at the central nervous system (CNS), which decreases the neural drive to the muscle.(4, 5)

The production of skeletal muscle force depends on contractile mechanisms, and failure at any of the sites upstream of the cross-bridges can contribute to the development of muscle fatigue, including nervous, ion, vascular and energy systems.(6)

For practitioners, athlete fatigue can be defined as the decrease in the pre-match/baseline psychological and physiological function of the athlete (7). Fatigue is a key metric for two distinct elite athlete management factors: tactical selection and the reduction in risk of athlete injury.

Sport specific “general athlete fatigue” is commonly identified through wearable GPS and accelerometer, reviewed in markers such as (a) speed decreases (b) reduced rates of acceleration and deceleration or (c) reductions in jump height, over either single practice times or over the course of a training cycle. The reason why this fatigue occurred, however, requires further interrogation by performance professionals to accurately diagnose and prescribe applicable training methods. Many practitioners are required to use additional technologies, such as Heart Rate Monitors (HRM) to acquire physiological data, in conjunction with off field measures such as a countermovement jump on a Force Plate to identify system changes. (8)

FATIGUE & INJURY 

While monitoring fatigue is important, research is vague in the area of correlating fatigue to both illness and injury, and part of the reason, it is speculated, is the lack of correlating technologies to form a diagnostic inference.

“A clear gap identified in the literature from the current review is the lack of assessment of load–fatigue interactions in association with injury/illness, as the fatigue state of an individual will essentially define the load they can tolerate before injury/illness risk increases”. (9,10,11)

In context for the general discussion, it is how NFL Wide Receivers fatigue during a game. “Skills” athletes, as these are designated in NFL circles, are required to run bouts of Olympic sprint speed repeatedly during the course of a game. (11) These speeds reach up to 23 MPH in games, and sometimes higher in practice as measured by GPS or similar (LPS- Local Positioning Systems) technology. Receivers must repeat these sprints up to and average of 17 times per NFL quarter, sometimes with little rest between efforts. Speed decrement due to athlete fatigue, particularly in the lower extremity, has been discussed as a cause of ‘late in game injury’ of players (12, 13). GPS data often confirms the “existence” of fatigue, but does not enable further data for interrogation as to why an athlete is moving or reacting slower or jumping lower. Comparative load measures arising from schedule changes are often inferred as causes for fatigue, but the underlying question of the biological system leading the onset of fatigue is “unknown”.

THE INTRODUCTION OF SENSE3 

Strive introduced the Sense3 product in a targeted release in 2020 to NFL, NBA and NCAA Teams in the United States. The sensor imprints are undetectable to the athlete wearing their preferred brand of compression shorts. EMG, Load and Physiological monitoring sensors are all contained in a single product and software offering.

THREE PRIMARY PHYSICAL SYSTEMS

World class athletes move differently than the normal population. In anaerobic field and court sport athletes, maximal power output is most predictive of elite performance.(14) For peak performance to occur, all athlete systems must be performing optimally. For this analysis, we will look at three primary physical systems for athlete performance which include:

• The Muscle Activation from the Visual and CNS Systems operating with competitive speed and accurate timing sequences to activate contractile patterns
• Kinematic Sequence is required for competitive environmental success
• Physiological Response system for the provision of

Measuring the primary physical systems of the athlete enables the practitioner to review not only systems as a whole, but also the effects on one another as possible reasons for change.

CORRELATION OR CAUSATION? AN INQUIRY 

In scientific review, causation is best defined as the capacity of one variable to affect another. This poses multiple questions for the practitioner, such as:

• Is higher Heart Rate and Physiological load leading the breakdown of muscle acquisition- firing and load?
• Is a time-based asymmetry and movement inefficiency leading to an increase in physiological demands?
• What are the degrees of asymmetry over time in the athlete?

And a very common question for athletes under GPS monitoring: Why is the athletes overall GPS measured load increasing with little to no change in practice volume?

The answers to these questions are specified by sport- position- and the individual athlete. Knowing the causation process and system degradations, however, enable a more focused adaptive training process to be modeled.

MUSCLE ACTIVATION, LOAD CHANGES, AND KINEMATIC ASYMMETRY 

Why did my athletes load score change?

As the former Senior Applied Sports Scientist for Catapult, in explaining the optic of the most utilized metric, “Player Load” (a summation of distance derived from GPS tracking, and aggregate data from accelerometers), many US Sports teams reviewed “Player Load Per Yard” for an understanding of the cost of tactical drills, and also to assemble a timestamp potentially on fatigue. Higher scores without field environmental change provided a guide to players who were becoming “less efficient”. “Why” is the obvious next question in interrogation of data, and inferences were left to be made from film and subjective athlete reporting.

Athlete movement efficiencies have been defined as displacement with lower measured “load” association. From a musculoskeletal viewpoint, lower load associations are functional to an efficiency in kinematic interactions, managed through a consistency of muscular activity.

Athlete asymmetries are a leading cause of non-contact injury in sports (15,16) A recent study provided by Strive reviewed the effects of fatigue on an individual’s performance, and the alteration over time of muscle loading, which correlates to changes in Player Load metrics.