Ballistic power: GPS-derived measurements suitable for the real-time monitoring of neuromuscular fatigue during repeated sprints

Power-force-velocity ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mi>F</mml:mi> <mml:mi>v</mml:mi> </mml:math> ) measurements have traditionally been employed to characterize the limits of an athlete’s neuromuscular system. However, in more recent years, there has been growing interest in whether <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mi>F</mml:mi> <mml:mi>v</mml:mi> </mml:math> metrics can also be used to define and assess training outcomes, e.g., as an indicator of performance and/or neuromuscular fatigue. Here we assess performance in a repeated sprint ability ( RSA ) test using traditional <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>P</mml:mi> <mml:mi>F</mml:mi> <mml:mi>v</mml:mi> </mml:math> measurements, alongside two novel metrics: ballistic power ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> ) and the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>F</mml:mi> <mml:mi>v</mml:mi> </mml:math> -offset, with the changes observed attributed to neuromuscular fatigue. Twenty-four physically active males (age = 26.08 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>±</mml:mo> </mml:math> 6.84 years) undertook the RSA test, consisting of 3 sets of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mrow> <mml:mn>5</mml:mn> <mml:mo>×</mml:mo> <mml:mn>50</mml:mn> </mml:mrow> </mml:math> m maximal sprints, with each participant wearing a STATSports Apex Pro series unit to track their motion. Mixed-effect models show how power-related metrics have the largest reduction due to fatigue compared to their force and velocity counterparts, with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> showing the largest decrease of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>∼</mml:mo> </mml:math> 31.8% ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>40.2</mml:mn> <mml:mo>≤</mml:mo> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> <mml:mo stretchy="false">(</mml:mo> <mml:mrow> <mml:mi mathvariant="normal">%</mml:mi> <mml:mspace width=".1em"/> <mml:mi mathvariant="normal">change</mml:mi> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≤</mml:mo> <mml:mspace width=".1em"/> <mml:mo>−</mml:mo> <mml:mn>23.4</mml:mn> </mml:math> , 95% CI, Cohen’s <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:mi>d</mml:mi> <mml:mo>=</mml:mo> <mml:mn>1.60</mml:mn> </mml:math> ) across the RSA test performed. We demonstrate that ballistic power, <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"> <mml:msub> <mml:mi>P</mml:mi> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">B</mml:mi> </mml:mrow> </mml:mrow> </mml:msub> </mml:math> , is the most reactive metric to athlete fatigue amongst the considered values. The described methods provide a promising, feasible tool for field-based monitoring of fatigue using routine GPS data.