This is caused by improper fit, a temporary problem with one - size diapers when baby is between sizes. (gobabygoshop.com)
This condition is much more present in cyclists in comparison to runners because of improper fit or some other fatigued muscle in the body. (fitnessandpower.com)
* Tips: Not having baby seated deeply in the baby carrier can result in improper fit. (babyslingsandcarriers.com)