AUTHOR=Ridard Jade , Rozand Vianney , Millet Guillaume Y. , Lapole Thomas 

TITLE=On-field low-frequency fatigue measurement after repeated drop jumps

JOURNAL=Frontiers in Physiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2022.1039616

DOI=10.3389/fphys.2022.1039616

ISSN=1664-042X

ABSTRACT=<p><bold>Purpose:</bold> Monitoring fatigue is now commonly performed in athletes as it can directly impact performance and may further increase the risk of injury or overtraining syndrome. Among the exercise-induced peripheral alterations, low-frequency fatigue (LFF) assessment is commonly restricted to in-lab studies. Measuring LFF on-field would allow athletes and coaches to assess muscle fatigability on a regular basis. The aim of the present study was therefore to validate a new portable device allowing quadriceps LFF assessment in the field.</p><p><bold>Methods:</bold> LFF was assessed in 15 active and healthy participants before (PRE) and after (POST) a series of drop jumps. LFF was assessed, thanks to a dedicated device recording evoked force to muscle submaximal electrical low- and high-frequency stimulation. Changes in the low- to high-frequency force ratio (further referred to as Powerdex<sup>®</sup> value) were compared to the changes in the ratio of evoked force induced by paired-pulse femoral nerve electrical stimulation at 10 and 100 Hz (i.e., DB10/DB100 ratio). Maximal voluntary contraction (MVC) and voluntary activation (VA) were also measured.</p><p><bold>Results:</bold> MVC decreased (<italic>p</italic> &lt; 0.001), whereas VA was not affected by the fatiguing task (<italic>p</italic> = 0.14). There was a decrease in the DB10/DB100 ratio (from 96.4% to 67.3%, <italic>p</italic> &lt; 0.001) as well as in the Powerdex value (from 74.0% to 55.7%, <italic>p</italic> &lt; 0.001). There was no significant difference between POST values (expressed in percentage of PRE values) of the DB10/DB100 ratio and Powerdex (<italic>p</italic> = 0.44), and there was a significant correlation between the changes in Powerdex<sup>®</sup> and DB10/DB100 (r = 0.82, <italic>p</italic> &lt; 0.001).</p><p><bold>Conclusion:</bold> The on-field device we tested is a valid tool to assess LFF after a strenuous exercise consisting of repeated drop jumps as it evidences the presence of LFF similarly to a lab technique. Such a device can be used to monitor muscle fatigability related to excitation–contraction in athletes.</p>