Walking or body weight squat "activity snacks" increase dietary amino acid utilization for myofibrillar protein synthesis during prolonged sitting.
Level 2 - randomized trial
Individual randomized crossover trial in humans
PubMed 35952344 · doi:10.1152/japplphysiol.00106.2022
What was done
Twelve healthy young adults (7 males, 5 females; age ~23 years; BMI ~25.1 kg/m²; baseline ~7,300 steps/day) completed three 7.5-hour crossover trials: uninterrupted sitting (SIT), sitting with intermittent walking every 30 minutes (WALK), and sitting with intermittent bodyweight squats every 30 minutes (SQUAT). Participants consumed two mixed-macronutrient meals (~55% carbohydrate, 30% fat, 15% protein) enriched with stable isotope tracers (L-[ring-2H5]phenylalanine or L-[ring-13C6]phenylalanine). Vastus lateralis biopsies were collected to quantify myofibrillar protein synthesis (MyoPS) via tracer incorporation and anabolic signaling protein phosphorylation via immunoblotting.
What was found
Plasma phenylalanine enrichment time course and area under the curve did not differ across conditions (P ≥ 0.78). MyoPS was significantly higher in SQUAT (0.103 ± 0.030%/h) and WALK (0.118 ± 0.037%/h) compared with SIT (0.080 ± 0.032%/h; P < 0.05). Compared to SIT, effect sizes were 0.75 (95% CI: -0.10 to 1.55) for SQUAT and 1.10 (95% CI: 0.20 to 1.91) for WALK. Fold change in rpS6 Ser240/244 phosphorylation was significantly greater in SQUAT versus SIT (7.6 ± 2.7 vs. 1.6 ± 0.45-fold, P < 0.05), with no significant differences observed between conditions for 4E-BP1, eEF2, mTOR, or ERK1/2 phosphorylation (P ≥ 0.21).
Why it matters
This study demonstrates that brief, low-barrier physical activity snacks during sedentary periods directly enhance the anabolic response of skeletal muscle to dietary protein. This provides a practical lifestyle strategy to stimulate muscle protein remodeling during prolonged daily sitting.
Limits
The study had a small sample size (n = 12) restricted to young, healthy individuals, limiting generalizability to older or metabolically impaired populations. The investigation assessed only acute 7.5-hour laboratory responses; long-term adaptations in muscle mass, strength, and chronic metabolic function were not evaluated.
Cited by
- supports Research from the Stanford Lifestyle Medicine group indicates movement breaks/snacks help maintain muscle mass.