Discussion
ankle sprains, fatigue
MINOR
In this study, we assessed postural stability, shuttle run performance, and jump height before and after a balance training intervention. All subjects performed the identical balance training, whereas the time before and after the balance training sessions varied between the groups. One group (HIIT-BALANCE) trained the balance tasks in a fatigued state, the other 2 groups (BALANCE and BALANCE-HIIT) in a unfatigued state. Our results on postural stability show that balance training under fatigue results in diminished improvements in postural sway compared with balance training in an unfatigued state, both when tested in the unfatigued and in fatigued states. This effect has been observed for all testing conditions, but with the effect being greatest when subjects were tested on the solid surface.The idea of considering “training under fatigue” is based on theoretical assumptions (Several previous studies reported a positive effect of balance training on the rate of force development (We monitored endurance capacity before and after the intervention period. As expected, an enhanced endurance performance was found for HIIT-BALANCE and BALANCE-HIIT when compared with BALANCE. The observed improvements (>10% in both HIIT groups) show that the HIIT intervention was an effective means to promote endurance performance. This observation is well in line with several previous studies reporting similar adaptations to HIIT (Endurance exercise does not only improve endurance performance but also has the potential to improve balance performance in healthy young to middle-aged adults (Despite great efforts in creating a solid study design, this study has some limitations. One limitation is that we could not randomize the testing sessions (fatigued vs. unfatigued). Because all measurements started with the unfatigued measurements, there could have been an order effect. In addition, we did not measure balance performance (i.e., sway paths) during the training sessions. Therefore, we do not know if balance performance was actually impaired during training when a HIIT protocol was performed before the balance tasks. Measuring indicators of fatigue such as rating of perceived exhaustion during assessments and trainings would also have been helpful in assessing the consistency of fatigue. However, these minor limitations do not have any influence on our research question—the question if “balance training under fatigue” should be recommended when aiming for a high neuromuscular performance in fatigued conditions. Based on our data, we can conclude (with some uncertainty because of the large confidence intervals) that training balance tasks in an unfatigued state results in enhanced training gains when compared with balance training under fatigue. However, these data on balance and jump do not allow any definite conclusions about the influence on injury risks. Therefore, future studies need to address the question whether and how these effects affect injury incidences of e.g., ankle sprains. Other minor limitations are that an inactive control group was not included and that no information was collected on the menstrual cycle. Acquiring this information would have been helpful for the interpretation of the balance adaptations because the menstrual cycle can have an influence on the neuromuscular control of ankle-stabilizing muscles (