Figure 1F is the reported levels of fatigue with the points for the fatiguing exercise shown in purple, and the points for the control exercise in green. There was a baseline measurement and five sets of exercises, and then recovery, with measurements of grip strength before and during the recovery period.
Throughout the number line, we provided six levels of fatigue as the mean to give participants a reference to the meaning of those numbers: “No Fatigue” (i.e., 0), “Mild Fatigue” (i.e., 20), “Moderate Fatigue” (i.e., 40), “Severe Fatigue” (i.e., 60), “Very Severe Fatigue” (i.e., 80), and “Worst Fatigue Possible” (i.e., 100).
Figure 1G is for the grip strength measurement after the fatiguing exercises. Grip strength as a percentage of baseline on the x axis, and reported fatigue is on the y axis (0 to 100). Look at the enormous variability in the reported fatigue after the exercise - it ranges from something like 10 to up to nearly 90. I really doubt that that variation can be attributable to levels of brain excitability. I would bet that it has more to do with cultural factors and variable interpretations of the question (i.e. does it just apply to the muscles that were used, or to a global assessment of fatigue. The datapoints for the two people who reported very high fatigue levels seem to me to be a bit dubious - and they are doing a lot of the heavy lifting in achieving a respectable r value in the regression of fatigue levels versus cerebellum excitability
Just to be clear, the participants were sitting in front of a computer and gripping a sensor hard with thumb and first finger for 5 lots of maybe around 35 seconds (see Figure 1c).
Participants held the force transducer between their thumb and index fingers of their dominant hand (see
Fig. 1B) and sat in front of a computer monitor that displayed their target force. As during the MVC task, the index finger was in a semi-flexed flexed position that facilitated the griping of the force sensor between the two digits. Force was exerted by pressing the force sensor against the thumb with index finger abduction. The target forces were 80% and 5% of participants' pre-MVC for the fatigue and control tasks, respectively. During the fatigue task, participants performed five isometric time-to-task failure (TTF) trials that required them to match the target force for as long as possible while the experimenter was verbally encouraging them to do so. The trial was terminated when the force exerted decayed <40% MVC for 3 consecutive seconds (
Hunter, 2018) (i.e., task failure point; see
Fig. 1C).
I did the 5 sets, just to see what it is like. At the end my global assessment of fatigue did not change, and I was able to type using my fingers nearly straight away. I would probably have chosen a fatigue rating specifically for my thumb and first finger of around 40% at the end of the sets, as did most of the participants. But, I feel a bit doubtful that what a relatively small part of my body was doing would affect cerebellum excitability significantly. This is particularly so because participants had to stop the 5 sets, and then report their level of fatigue, and then do a strength test, and then their cerebellum excitability was assessed. Possibly the test of motor control was also done prior to the cerebellum excitability test. My fingers were only fatigued for a minute or so, so I'm pretty sure that by the time the cerebellum excitability test was done, there would not have been much impact from the exercise.
So, I'm not sure about the assumptions built on the fatigue rating data and therefore about the conclusions of the study. Maybe the study could be repeated looking at people doing a marathon, that way the researchers could be more sure that the participants really were fatigued.
