Effects of protein drink temperature on leg muscle strength and muscle mass during a 4-week training period: A pilot study

Adequate post-exercise protein intake supports muscle recovery. Studies showed that hot drinks accelerate gastric emptying and enhance nutrient absorption. However, the effect of drink temperature on muscle strength and mass remains unclear. Therefore, this study conducted a 4-week intervention study and an acute study focusing on digestion rate. In Study 1, a 4-week parallel-group trial was conducted in 38 healthy adults without exercise habits, assigned to either a Cold ( < 10°C) or Hot (60°C) group. Participants consumed a 250 mL of protein drink daily at the designated temperature and performed 30 minutes of leg strength training three times per week. Knee extensor strength and leg muscle mass were assessed before and after the intervention. In Study 2, the effect of 200 mL of a protein drink temperature (4 or 60°C) on gastric emptying rate was investigated using ¹³C stable isotope breath test. In Study 1, an analysis of covariance, with pre-intervention values as covariates, revealed a significant group effect on post-intervention knee extensor strength in the right leg, with the Hot group showing 12% higher strength (35.7 ± 1.3 kgf, mean±standard error) compared to the Cold group (31.4 ± 1.2 kgf) (p = 0.017). There was no significant difference in muscle mass between the groups. In Study 2, the initial ¹³CO₂ excretion rate was higher in the Hot group (p < 0.001). The findings of this study suggest that the temperature of protein drinks may modestly influence early-phase digestion and may have a limited impact on muscle strength in individuals without regular exercise habits.