Although alpha/beta angles remained consistent on the flat surface and on the Bosu barefoot, when on the Bosu with trainers they were far less stable. The ankle complex contributes significantly to support and aids in power generation during squats (Hung & Gross, 1999). Normal range of motion about the subtalar joint is approximately 5° for eversion and inversion (Clarkson & Gilewich, 1999). Limited ankle mobility can often lead to the heels lifting off the floor and excessive foot pronation/supination, which has been described as anything outside of 5° (Clarkson & Gilewich). Squats performed with trainers on the Bosu reached between 15 to 20° which far exceeded the normal range as previously stated. This might leave participants particularly vulnerable to injury as the subtalar joint would be in a plantar flexed, inverted position (Baumhauer et al., 1995). However, Beynnon et al. (2002) found that anatomic foot type does not appear to be a risk factor for ankle injuries. Nevertheless, in order to maintain correct technique and reduce the likelihood of injury, athletes should look to avoid excessive pronation and supination of the ankle, therefore removing trainers when on an uneven surface could be beneficial.
Finally, literature has reported that athletes are advised not to wear trainers or running shoes when squatting as they do not provide enough support when pushing through the mid-foot/heel (Sato et al., 2012). This could be seen as a limiting factor of the current study. However, for use in practical environments where athletes are likely to perform squatting movements in trainers or equivalent, it does help to provide an insight into the angles of the foot which might aid with potential interventions that could be put into place. Another limitation of the study is that angles were only recorded at the bottom of the squat from the side and 0%, 25%, 50%, 75% and 100% from the back view. Although these attempted to identify the key elements of the squat, it would be beneficial to measure angles throughout the whole movement. Future studies could look to analyse angles at a greater number of points throughout the squat and determine the effect that other types of footwear might have on joint and segment angles when squatting on the Bosu or equivalent. Also, it may be beneficial for studies to control certain aspects of the squat. For example foot placement and squat depth should be monitored to ensure less variation.
The results of the study suggest that squatting on an uneven surface can alter joint and segment angles to potentially damaging positions, however it can also act to control certain aspects. Squatting barefoot can help to minimise this and would be recommended in order to facilitate correct technique and reduce the chance of injury, although this can depend on the individual. Ultimately, correct technique should be followed by athletes/practitioners and utmost effort should be applied to ensure that injury risk is minimised when performing a squat, particularly when excessive force is being applied.
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