Intervention Period
motor or cognitive dual, motor or cognitive dual tasks, fatigue
All 3 groups performed the identical balance training intervention. The intervention lasted for 6 weeks with a total of 12 training sessions. The volunteers trained twice a week with at least 48 hours between training sessions. Subjects trained on 4 different devices: wobble board, tilt board, soft mat, and air cushion. The subjects performed 4 trials of 20 seconds on each device and leg leading to a total of 32 trials per session. To avoid fatigue, 25 seconds of rest were given between 2 consecutive trials. There was a rest period of approximately 1 minute between the devices, resulting in a duration of approximately 30 minutes per session. All sessions were supervised. The difficulty of the balance tasks was continuously adjusted to the individual and actual performance level. At the beginning of the training, all subjects performed the balance tasks with eyes open (Level 1). If the tasks of level 1 could be solved without problems, the subjects were asked to train the next difficulty level (level 2: eyes open with motor or cognitive dual tasks such as counting backward or catching or passing a ball; level 3: eyes closed; level 4 eyes closed with motor or cognitive dual tasks). The different levels allowed an individualized and continuous progression of the task difficulty during the intervention period.Although the BALANCE group trained balance tasks only, the other 2 groups additionally completed a fatigue protocol either before or after the balance tasks. In the HIIT-BALANCE group, the fatigue protocol was performed before the balance exercises and thus corresponded to a “balance training under fatigue.” By contrast, the BALANCE-HIIT group trained first the balance tasks and directly afterwards the fatigue protocol. Thus, the acute fatigue could not have influenced balance performance in this group. The fatigue protocol was a HIIT session with subjects running on an athletics track. Each HIIT session involved 4*4 minutes of high-intensity intervals with a heart rate above >90% of the individual maximum heart rate, interspersed with 3 minutes of active recovery (heart rate ∼60% of maximum heart rate).