Sample size justification: A sample size of 30 per group is in line with recommendations for pilot studies where the aim is to determine the feasibility of a future efficacy study by estimating the treatment effect (for a power calculation) and estimating rate of non-completion of the intervention. A minimum total sample size of 50 (i.e. 25 per group) is recommended to allow for a precise estimate of the pooled standard deviation at the post intervention assessment. Increasing the number to 30 per group allows for non-completion of up to 20%. Furthermore, a sample size of 30 per group allows for an acceptably precise estimate of the non-completion rate; a 95% confidence interval less than +/-11% for completion rates of 80% or higher.