In medical studies, treatments are tested within a group of study participants. You will be given a sentence of a study report in which your task is to list the phrases that give information about the participants of the study. You should list the phrases in the same order that they appear in the text, separated by commas. If no information about the participants is mentioned, just output "not found". Relevant information about participants include: gender, medical conditions, location, number of people participating. Do not contain participant mentions without relevant information.

To study the effects of physical exercise on biochemical risk factors for ischaemic heart disease 31 healthy middle aged men undertook regular physical exercise for two months and 29 served as controls in a randomised trial .
31 healthy middle aged men

For the QoL-Colostomy , however , there was no significant difference between the control and experimental groups .
not found

Although an increasing number of group-based programs for the improvement of social skills have been described , randomized controlled trials are needed to evaluate their efficacy .

not found