Whey protein isolate attenuates strength decline after eccentrically-induced muscle damage in healthy individuals
Journal Title (Medline/Pubmed accepted abbreviation): J. Int. Soc. Sports Nutr.
Year: 2010
Volume: 7
Number: 30
Page numbers:
doi (if applicable): 10.1186/1550-2783-7-30

Summary of Background and Research Design

Background: Whey protein has been shown to be beneficial following strength training routines for the purpose of gaining muscle, quickening recovery, and reducing soreness. In particular, hydrolyzed whey protein isolate is efficiently absorbed and delivered to damaged muscle cells.
In eccentric exercise, the contracting muscle is forcibly lengthened (e.g., resisting a weight while it is being lowered), whereas in concentric exercise, the muscle shortens. Eccentric exercise is a key cause of muscle damage and the soreness that follows exercise.

Hypothesis/Research Question: Does supplementation with hydrolyzed protein for 14 days accelerate muscle recovery in untrained males?

Subjects: 17 healthy, untrained males, 23 ± 5 yrs old, mean body weight = 77 kg for CHO group, 81 kg for whey protein group.

Experimental design: Parallel group, randomized, double-blind, placebo-controlled study

Treatments and protocol:Before the study, the participants familiarized themselves with the exercises and a one-rep maximum weight (1RM) was determined for isokinetic knee flexions and isokinetic/isometric knee extensions. During “damage sessions”, leg curls and leg extensions were completed at 120% of the participants' predetermined 1RM. They performed 4 sets of 10 at a 4 sec cadence with 3 min in between sets. After the “damage session”, subjects received 1.5 g/kg body weight/day of either a whey protein hydrolysate supplement (WPH; ~120 g 90% whey protein supplement per day, for an 80-kg subject, containing 108 g protein, 10.6 g carbohydrate, and 2.4 g fat) or isocaloric carbohydrate (CHO; 120 g dextrorotatory glucose crystals; ) The supplements were consumed within 30 min of the exercise session. Blood samples were collected 30 min; 1, 2, 4, and 24 hrs; and 2, 3, 4, 7, 10, and 14 days after the damage session. Measures of strength for 3 exercises (isokinetic knee flexion, isometric/isokinetic knee extension) were taken at 1 2, 3, 4, 7, 10, and 14 days after the damage session. On the days following the damage session, participants would consume the same dose of the supplement, but it was distributed in 4 equal doses (~30 g each) throughout the day.

Summary of research findings:
  • WPH supplementation immediately exercise attenuated the reduction in strength the next day (isometric extension) and in subsequent days until full strength was recovered.
  • WPH supplementation caused muscles to be back to “100%” in about 4-7 days, as opposed to the carbohydrate supplement, where it took 10-14 days (g.e., isometric knee extension).
  • Creatine kinase (CK) and lactate dehydrogenase (LDH) activity increased in both groups 2-4 days into recovery, but these markers increased less in the WPH group. These biomarkers imply that the muscle damage was less extensive in the group supplemented with WPH or that muscle protein synthesis was increased more in the WPH group to counteract the damage.

Interpretation of findings/Key practice applications:

  • Untrained muscles can recover faster and maintain more strength when a whey protein hydrolysate supplement is ingested within 30 min post-workout and at frequent daily intervals for two weeks compared with an isocaloric amount of carbohydrate.

Limitations of the research:

This conclusion may not be applicable to trained athletes, who already experience considerable adaptation to muscle damage and soreness due to exercise. It is also uknown if other types of protein would produce results similar to those of whey protein, or if smaller amounts of protein would be just as effective.
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