Separate Effects of Intensity and Amount of Exercise on Interindividual Cardiorespiratory Fitness Response.
Level 2 - randomized trial
Individual randomized controlled trial
PubMed 26455890 · doi:10.1016/j.mayocp.2015.07.024
What was done
Sedentary, middle-aged (mean age 53.2 years), abdominally obese adults (n=121; 75 females) who completed at least 90% of 5 weekly exercise sessions over a 24-week intervention were randomized into three groups: (1) low-amount, low-intensity exercise (LALI; 180 kcal/session for women, 300 kcal/session for men at 50% of VO2peak; n=39); (2) high-amount, low-intensity exercise (HALI; 360 kcal/session for women, 600 kcal/session for men at 50% of VO2peak; n=51); or (3) high-amount, high-intensity exercise (HAHI; 360 kcal/session for women, 600 kcal/session for men at 75% of VO2peak; n=31). Cardiorespiratory fitness (CRF) was measured using treadmill tests at 4, 8, 16, and 24 weeks.
What was found
CRF increased within all three groups at 24 weeks (P<.001). At 24 weeks, the proportion of CRF nonresponders was 38.5% (15 of 39) in LALI, 17.6% (9 of 51) in HALI, and 0% (0 of 31) in HAHI. At a fixed intensity, increasing exercise amount reduced the rate of nonresponse by 50% (P=.02). At a fixed high amount, increasing exercise intensity eliminated nonresponse (P=.001). The number of nonresponders plateaued between 4 and 8 weeks for LALI and by 16 weeks for HALI, but decreased continuously over 24 weeks for HAHI.
Why it matters
This study shows that apparent nonresponse to exercise training in cardiorespiratory fitness is modifiable by increasing exercise volume or intensity rather than being an immutable individual trait.
Limits
The analysis is restricted to participants who completed at least 90% of exercise sessions, introducing potential compliance bias. The abstract does not define the exact threshold used for nonresponse, lacks a non-exercising control group, and evaluates only sedentary adults with abdominal obesity.
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