Interpretting Fatigue Data: Methods Matter!

A well-researched topic in the Exercise Science world is muscle fatigability due to its relevance in the athletic population in regards to increased risk of injury. Numerous studies have attempted to quantify fatigue using various methods, but there is a gap in research regarding which method most accurately depicts this decline in strength as it relates to torque production. In a recent study published in The Open Sports Sciences Journal by Ciccone and colleagues, they attempt to fill this gap by examining how the method used effects data interpretation and which methods seem to be best.

In this study, 18 healthy males and females performed 50 maximal effort knee extensions using an isokinetic dynamometer (Biodex). Participants were familiarized with how the machine works, and practiced performing knee extensions from 90° knee flexion to 180° (full extension) prior to the experimental trial. Fatigue was measured using two methods – calculation of a fatigue index and calculation of torque slopes. Fatigue index was calculated using the following equation: [(initial torque – final torque)/initial torque]x100. Initial torque was selected from one of the following values: average of first 3 reps, average of first 5 reps, highest 3 rep average, or highest 5 rep average. The final torque was selected from either the last 3 or last 5 reps. Data was collected over 30 reps and 50 reps, because of the commonality of these two values in research. Both isokinetic load range and the angle at which peak torque is produced was recorded for each trial.

This study produced several outcomes of interest, mainly confirming the complexity of measuring muscle fatigue as it relates to torque production and the multiple variables you must consider. Firstly, depending on which torque variable you use (initial, end, peak etc) you will get varying calculations of fatigue index. Rather than using the first 3 reps which would lead to an underestimation of fatigue, this study found that using the peak 3 or peak 5 reps provided a much better representation of decline in strength. In addition, instead of estimating a potential range of motion in which its most likely the individual will produce maximum torque, this study found it’s better to look at torque throughout the full range of motion due to the variability in knee angle at which peak torque production occurs especially with fatigue. Lastly, studies that look at slope of torque to measure fatigue should focus on repetitions following the rep at which peak torque was produced, instead of focusing on the first few reps in order to avoid underestimating fatigue.

Looking at the big picture, perhaps we need to be more consistent and precise about which methods are used in research examining muscle fatigue and force production via isokinetic dynamometry so that the data we interpret is reliable enough to draw conclusions from and incorporate into our clinical judgement as it relates to high level athletes.