JMIR Publications

ABSTRACT

Background:

Research have found that the longer sedentary time, the higher the risk of all-cause mortality and cardiovascular diseases. Traditional physical activity and training can reduce the harm caused by sedentary behavior but cannot completely counteract it, but they additionally carry risks such as joint injuries, sudden hypertension, and other exercise-related risks, as well as limitations in terms of time and space. “Exercise snacks”—short, frequent bouts of physical activity throughout the day—have become a potential solution to sedentary behavior due to their universal applicability in time and space. However, the relationship between exercise dosage, response, as well as strategies for precise population adaptation, have yet to be systematically quantified.

Objective:

We set out to chart how short, scattered bouts of activity influence health in sedentary adults, to pin down the minimum daily frequency needed for meaningful gains in fitness, metabolism and muscle function, and to see whether age or metabolic status alters the recipe.

Methods:

A scoping review based on the PRISMA-ScR guidelines was conducted, searching the PubMed, Web of Science, and EBSCO databases until August 25, 2025. A total of 15 randomized controlled trials (RCTs, n=1255) were included, covering healthy adults (46.7%), populations at metabolic risk (including obesity/type 2 diabetes (T2DM), 33.3%), and the elderly (20.0%). Exercise dosage parameters were defined through three dimensions: minimum threshold, physiological indicators, and physiological responses/core pathways.

Results:

High-intensity exercise performed 3-6 times daily, with each session lasting ≤1 minute, significantly improved cardiovascular and respiratory function in sedentary individuals. Peak oxygen uptake (VO2peak) increased by 5% (P < 0.05); maximal oxygen uptake (VO2max) improved by 4.47 mL/kg/min (P < 0.05). Interrupting sedentary time every 30-60 minutes to optimize metabolic health, such as with chair squats or stair sprints, resulted in a 14-18% decrease in postprandial insulin levels (P < 0.05); visceral fat was reduced by 30% (P < 0.05). Low-frequency resistance training improved muscle adaptability, with lower body training and mixed training increasing muscle mass by 0.42-1.2kg (P ≤ 0.01) and enhancing lower body strength by 11% (P < 0.01).

Conclusions:

Exercise snacks, through frequent short-duration interventions, effectively improve cardiovascular, metabolic, and muscle health, offering advantages of high adherence and low risk. This study systematically establishes the exercise dosage-response relationship for the first time and, based on RCT data, introduces the “3-8-2” frequency threshold (≥3 times/day for cardiovascular improvement, ≥8 times/day for metabolic enhancement, ≥2 times/day for muscle adaptation). It also provides a precise prescription for sedentary populations: desk squats for office settings, high-frequency stair sprints for those with metabolic abnormalities, and “strength + Tai Chi” mixed training for the elderly. Clinical Trial: Not applicable