Sports bras are meant to control and reduce breast movement in order to prevent injury and discomfort. A poorly fitting bra, which is not providing adequate support, can not only cause discomfort during your parkrun, it can cause irreversible damage to the breast tissue and even impact your performance. Uncontrolled breast movement could also lead to a four centimetre reduction in stride length; this roughly equates to completing an additional 200 metres over the course of a parkrun.

Breast tissue does not contain any muscle to help control excessive motion – this means the delicate tissue structures can become irreversibly stretched and damaged if not sufficiently supported.

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Source: Parkrun