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Effects of soluble milk protein or casein supplementation on muscle fatigue following resistance training program: a randomized, double-blind, and placebo-controlled study

Abstract (provisional)

Background: The effects of protein supplementation on muscle thickness, strength and fatigue seem largely dependent on its composition. The current study compared the effects of soluble milk protein, micellar casein, and a placebo on strength and fatigue during and after a resistance training program.

Methods: Sixty-eight physically active men participated in this randomized controlled trial and underwent 10 weeks of lower-body resistance training. Participants were randomly assigned to the Placebo (PLA), Soluble Milk Protein (SMP, with fast digestion rate) or Micellar Casein (MC, with slow digestion rate) group. During the 10-week training period, participants were instructed to take 30 g of the placebo or protein twice a day, or three times on training days. Tests were performed on quadriceps muscles at inclusion (PRE), after 4 weeks (MID) and after 10 weeks (POST) of training. They included muscle endurance (maximum number of repetitions during leg extensions using 70% of the individual maximal load), fatigue (decrease in muscle power after the endurance test), strength, power and muscle thickness.

Results: Muscle fatigue was significantly lower (P < 0.05) in the SMP group at MID and POST (-326.8 +/- 114.1 W and -296.6 +/- 130.1 W, respectively) as compared with PLA (-439.2 +/- 153.9 W and -479.2 +/- 138.1 W, respectively) and MC (-415.1 +/- 165.1 W and -413.7 +/- 139.4 W, respectively). Increases in maximal muscle power, strength, endurance and thickness were not statistically different between groups.

Conclusions: The present study demonstrated that protein composition has a large influence on muscular performance after prolonged resistance training. More specifically, as compared with placebo or micellar casein, soluble milk protein (fast digestible) appeared to significantly reduce muscle fatigue induced by intense resistance exercise.

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Alex’s Notes: Milk has two forms of protein: soluble and rapidly digestible proteins such as whey, and slowly digesting micellar casein. Muscle protein synthesis (MPS) has been shown to be greater with whey compared to casein. However, we know that MPS doesn’t translate into long-term adaptations, and we also know that the effects of protein supplementation depend largely on the protein’s composition. The aim of this brief study was simply to compare the effects of micellar casein and a soluble milk protein (whey) on muscle performance after a 10-week resistance training program.

The subjects included 68 males that were engaged in 2-6 hours of physical activity per week, but none of which was aimed at increasing the quadriceps size or strength. Moreover, they were all healthy and anyone who was taking any dietary supplement, sports drink, or functional food intended to enhance performance or muscle mass, or had taken any of these in the previous month, were excluded. They trained three times per week on the leg extension, leg press, and leg curl machines in a periodized manner. They were randomized to receive a micellar casein supplement, Prolacta (whey), or a placebo. On non-training days, they took their protein supplement upon waking and before bed, and on training days they took the protein supplement three times: in the morning and 30 minutes before and after training.

Now, you would think the above is adequate given that protein timing has some credible research supporting it. However, each protein supplement serving was only 10g, meaning the subjects only received an additional 20g of protein on non-training days and 30g of protein on training days. Regardless, the novice weight-lifters used their newbie gains to increase muscle endurance and 1RM strength equally between groups. Muscle thickness also increased equally.

But whey still came out on top. Despite the above similarities in a few adaptations, the whey (Prolacta) group had significantly enhanced muscle endurance, reduced fatigue, and slightly enhanced recovery when compared with casein. So go whey.

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