Casein and whey protein in milk protein contain all essential amino acids required to effectively stimulate muscle protein synthesis while carbohydrates inhibit protein breakdown due to augmented insulin secretion.
The authors of the current study, published in 'Nutrients', say it is unknown how these effects of protein and carb intake on muscle protein balance translate in reducing exercise induced muscle soreness and muscle damage and whether increasing protein intake after exercise is superior to carbs.
In this double-blind, placebo-controlled intervention study, funded by FrieslandCampina, researchers compared the effects of an optimised protein supplementation protocol (20 g milk protein with 20% whey protein, 80% casein post-exercise and during breakfast and 40 g milk protein prior to sleep) to iso-caloric carbohydrate supplementation on exercise-induced muscle soreness and other markers of muscle damage.
They expected to find that those consuming protein supplements would suffer less muscle soreness and damage.
However, they found no greater benefit of protein supplementation on muscle soreness and other muscle damage markers after a 15-km road race compared to the group that received carbohydrate supplementation.
In fact, higher quadriceps pain thresholds were found in the carbohydrate group as well as comparatively low muscle soreness one day post-race.
The researchers enrolled 323 men and women (aged 25-65) registered for the 15 km Seven Hills Run (18 November 2018), in the Netherlands. Participants were randomly allocated to either the protein supplement or the CHO placebo supplement group.
Baseline muscle soreness was questioned, dietary intake was determined using 24-h recalls, and information about demographics and exercise training characteristics were collected. Finish times were collected and average heart rates during the race were collected from participants that ran with a heart rate monitor.
Participants received their supplements directly after the race, prior to sleep and during breakfast, until three days post-race and they filled out questionnaires about muscle soreness at one, two, and three days post-race.
Within a subgroup of 75 participants of the protein group and 74 participants of the placebo group, objective muscle soreness was measured with a strain gauge algometer at 25–48 hours post-race.
Blood concentrations of creatine kinase (CK) and lactate dehydrogenase (LDH) were also assessed in this subgroup to determine muscle damage.
The protein group reported similar muscle soreness compared to the placebo group and similar muscle damage markers were observed. Within the placebo group however, higher quadriceps pain thresholds were found compared to the protein group and the placebo group reported comparatively low muscle soreness on one day post-race, but not on days 2 and 3.
Discussing possible reasons for these results, the researchers note the habitual protein intake (protein group: 1.11 ± 0.33 g protein per kg/d, placebo group: 1.17 ± 0.37 g/kg/d) was already sufficient among the studied participants and this may have meant the protein supplementation could not result in a superior effect above their normal diet.
They also point out the results are in-keeping with prior studies showing that carbs can improve muscle protein balance because of the increased insulin secretion which inhibits protein breakdown. Co-ingestion of carbohydrates with protein synergistically has been shown to augment insulin secretion and improves muscle protein balance because of the increased amino acid availability and delivery to the muscle compared with ingestion of carbohydrates alone.
Hopman. M. T .E., et al
https://doi.org/10.3390/nu13030858 (registering DOI)