The authors concluded that generally there were no differences in adherence to exercise when different frequencies, intensities, durations and modes of physical activity were prescribed, although the results were not robust. Given limitations in the review methodology and the unknown quality of the included studies, the reliability of the results are unclear.

To assess the effect of physical activity guideline characteristics on behavioural adherence.

PubMed, Web of Science, PsycINFO and SPORTDiscus were searched up to November 2007. Search terms were reported. Reference lists of relevant publications were checked. Only English-language publications in peer-reviewed journals were included; dissertations, theses and conference proceedings were excluded.

Randomised controlled trials (RCTs) that evaluated physical guideline characteristics (frequency and/or intensity and/or duration and/or mode of activity) on behavioural adherence in adults 18 years of age or older were eligible for inclusion. Studies that measured participant retention only were excluded from the review.

The included trials evaluated a number of different exercise programmes (such as uphill treadmill walking, jogging, aerobics, walking, cycling and video workouts). The trials included participants from various age groups (primarily middle-aged adults) and included either men or women or both. Where reported, participants were described as healthy, sedentary, obese or menopausal. Adherence was measured using a polar heart rate monitor, attendance, self-report activity log, accelerometer or a Borg rate of perceived exertion scale.

The authors did not state how the papers were selected for the review.

It appeared that study quality may have been assessed, but no details were reported. The authors commented on how many studies used intention-to-treat-analysis.

The authors stated that effect sizes were calculated for each study where possible. When studies reported data from multiple time points, the results were averaged.

The authors did not state how many reviewers performed the data extraction.

The authors used a vote-counting procedure to summarise the results. The authors calculated effect sizes where data were available using the following criteria to assess the magnitude of the effect: <0.20=trivial; 0.20=small, 0.50=medium and 0.80=large. Where possible, meta-analyses were conducted to pool effect sizes using a random-effects model.

Twenty-seven RCTs (n=2,632) were included in the review.

Five of seven trials that compared different frequencies of weekly physical activity reported no significant differences in participant adherence to exercise; two trials reported significantly better adherence when low-frequency activities were prescribed. An overall effect size of 0.08 was reported (six trials, n=989) that favoured lower frequency activities over higher frequency activities.

Twelve trials compared different intensities of physical activity; nine trials reported no difference in participant adherence to exercise by degree of intensity. An overall effect size of 0.02 was reported (10 trials, n=1,472) that favoured high-intensity activities compared to moderate-intensity activities.

Fifteen trials compared different durations of physical activity; seven trials reported no difference in participant adherence to exercise when different exercise durations were compared. An overall effect size of 0.05 was reported (seven trials, n=975) that favoured higher duration physical activities compared to lower duration activities. Five trials evaluated whether the accumulation of daily activities in 10-minute bouts differed from a single sustained bout of exercise. An overall effect size of 0.13 was reported (n=287) that favoured a sustained bout of activity.

Ten trials compared different modes of physical activity on participant adherence to exercise. Generally, there were no significant differences between the comparators: aerobic activities versus resistance training, exercise versus lifestyle activities and walking versus running. Effect sizes were reported that favoured aerobic activity (0.01), lifestyle activities (0.09) and running (0.03) (sample sizes not reported).

Generally, there were no differences in adherence to exercise when different frequencies, intensities, durations and modes of physical activity were prescribed, although the results were not robust.

The review addressed a clear question and was supported by appropriate inclusion criteria. The search was restricted to English-language publications, which introduced potential for publication and language biases. The methods used to assess study quality (if assessed) were not reported. The authors did not state how many reviewers were involved in the review process, thus reviewer error and bias may have been introduced. Details of the included studies were presented in tables.

Given the clinical heterogeneity between studies, limitations in the review methodology and the unknown quality of the included studies, the reliability of the results are unclear.

Practice: The authors stated that exercise prescription by practitioners can be based around the health-related fitness and safety goals of the patient.

Research: The authors stated that more research was needed to establish whether total duration of prescribed physical activity affected programme continuation, that high-quality research was needed to assess the role of activity type on physical activity adherence and that research was needed on single bouts of exercise.

Not stated; the authors were supported by research grants.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.