In reviewing this article we made several observations that should be brought to the attention of Vissers et al. and your readers.

Findings from our own study, the Alberta Physical Activity and Breast Cancer Prevention trial (ALPHA), described by Friedenreich et al. [1], were included in this review as were those from a similar trial described by Irwin et al. [2] known as the Physical Activity for Total Health (PATH) study. In Table 1 of the article by Vissers et al., the frequency of exercise in ALPHA is shown as 3.6/week vs. in PATH as 5/week, and the intensity of exercise in ALPHA is reported as 62% heart rate reserve vs. in PATH as 60-75% HRmax. Furthermore ALPHA is characterized as an "aerobic" exercise intervention vs. PATH which is described as a "combination" exercise intervention.

However the prescribed exercise interventions in these trials were very similar:

ALPHA trial: 45 min/day, 5 days/week, supervised & home-based; mainly aerobic exercise (Table 2 in [3] describes specific activities); at least half of each workout @ 70-80% heart rate reserve to be achieved by week 12.

PATH trial: 45 min/day, 5 days/week, supervised & home-based; mainly aerobic exercise (Table 2 in [2] indicates that 0.4% & 5.8% of supervised and home exercise, respectively, was strength training), 60-75% HRmax to be achieved by week 8.

Also the level of exercise attained by the exercise groups in these two trials was similar:
ALPHA: mean, 3.6 d/week, 178.5 min/week [3]
PATH: mean, 3.5 d/week, 176 min/week [2]

We are concerned that the inconsistent method of data extraction used by Vissers et al. might explain why the similar results for the ALPHA and PATH trials seemed “surprising” to the authors, as noted in their Discussion on "Training Volume". The authors reason that adherence might have been over-reported in the Irwin trial, but it appears that Vissers et al. reported the prescribed exercise for the Irwin trial, not adherence.

Furthermore Vissers et al. describe a subgroup meta-analysis that combines data from the PATH and STRRIDE-AT/RT trials [4], which they characterize as the only “combination” training interventions in their review. However, readers should note the heterogeneity between these trials; in the PATH study most exercise was aerobic; only 0.4% & 5.8% of supervised and home exercise, respectively, was classified as strength training [2]. In contrast, the three-armed STRRIDE-AT/RT trial (which compared aerobic vs. resistance vs. aerobic/resistance exercise arms) involved proportionately more resistance exercise than PATH [4]. For this reason it is our opinion that data from the STRRIDE-AT/RT trial provides a clearer picture of the effects of combined exercise training than this particular subgroup meta-analysis.

We would also like to point out that in the forest plots for Figures 2 & 4, we could not find a reference for the study labeled Irwin, 2011 but suspect this might refer to Irwin, 2003 [2].

Respectfully,
Heather Neilson, MSc
Christine Friedenreich, PhD
Department of Population Health Research, CancerControl Alberta
Alberta Health Services
Calgary, Alberta, Canada

1. Friedenreich CM, Woolcott CG, McTiernan A et al. Adiposity changes after a 1-year aerobic exercise intervention among postmenopausal women: a randomized controlled trial. Int J Obes (Lond). 2011;35(3):427-435.

2. Irwin ML, Yasui Y, Ulrich CM et al. Effect of exercise on total and intra-abdominal body fat in postmenopausal women: a randomized controlled trial. JAMA. 2003;289(3):323-330.

3. Friedenreich CM, Woolcott CG, McTiernan A et al. Alberta physical activity and breast cancer prevention trial: sex hormone changes in a year-long exercise intervention among postmenopausal women. J Clin Oncol. 2010;28(9):1458-1466.

4. Slentz CA, Bateman LA, Willis LH et al. Effects of aerobic vs. resistance training on visceral and liver fat stores, liver enzymes, and insulin resistance by HOMA in overweight adults from STRRIDE AT/RT. Am J Physiol Endocrinol Metab. 2011;301(5):E1033-1039.