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Table 1 Summary of studies meeting inclusion criteria

From: The effect of protein timing on muscle strength and hypertrophy: a meta-analysis

Study Subjects Supplementation Protein matched with control? Anthropometric and/or body composition assessment method Training protocol Strength results Body composition results
Antonio et al., [33] 19 untrained young women 18.3 g EAA or an equal dose of cellullose placebo taken (collectively) 20 minutes pre and post-exercise No DXA Periodized progressive resistance training consisting of exercises for all major muscle groups performed 3 days/wk for 6 wks Total weight lifted at the 12 RM intensity did not significantly change in either group No significant body composition changes occurred in either group
Goddard et al., [34] 17 untrained older men (60–80 y) 12 g of essential amino acids and 72 g (total) of fructose and dextrose consumed immediately after exercise No Computed tomography (CT). Progressive resistance training consisting of knee extensions preformed 3 days/wk for 12 wks Training produced a significant increase in 1RM strength and measures of maximal torque, no differences between groups No significant differences in muscle CSA increase between groups
Rankin et al., [35] 13 untrained young men Chocolate milk (providing a protein dose of 0.21 g/kg) or a CHO-electrolyte beverage (Gatorade) immediately after exercise No Dual X-ray absorptiometry (DXA) and multiple upper & lower body circumference measurements Periodized progressive resistance training consisting of exercises for all major muscle groups performed 3 days/wk for 10 wks 1 RM strength increased in all exercises, with no significant difference between groups No significant differences in fat reduction, mean mass gain, or circumference changes between groups
Andersen et al., [36] 22 untrained young men 25 g protein (combination of whey, casein, egg white, and glutamine) or 25 g maltodextrin immediately before and after exercise No Muscle biopsy Periodized progressive resistance training consisting of lower body exercises performed 3 days/wk for 14 wks Squat jump height increased only in the protein group, whereas countermovement jump height and peak torque during slow isokinetic muscle contraction increased similarly in both groups. The protein group showed hypertrophy of type I & II muscle fibers, whereas no significant change occurred in the CHO group
Bird et al., [37] 32 untrained young men 6 g EAA or 6% CHO solution + 6 g EAA or placebo during exercise No DXA and muscle biopsy Progressive resistance training consisting of exercises for all major muscle groups performed 2 days/wk for 12 wks Training caused a significant increase in 1RM in the leg press similarly in both treatment groups compared to placebo, isokinetic strength increased in all groups, with no differences between groups CHO + EAA showed greater gains in fat-free mass compared to placebo, fat mass decreased in all groups without any significant difference between groups
Coburn et al., [38] 33 untrained young men 20 g whey + 6.2 g leucine or 26.2 g maltodextrin 30 minutes prior to and immediately after exercise No Magnetic resonance imaging (MRI) Progressive resistance training consisting of knee extensions performed 3 days/wk for 8 wks Significantly greater 1 RM strength increase in the trained limb in the protein group compared to placebo No significant body composition changes occurred in any of the groups, CSA increases did not differ between the protein and placebo groups
Candow, Burke, et al., [39] 27 untrained young men & women Whey (1.2 g/kg) + sucrose (0.3 g/kg) or placebo (1.2 g/kg maltodextrin + 0.3 g/kg sucrose) No DXA Progressive, periodized resistance training consisting of exercises for all major muscle groups performed 4 days/wk for 6 wks 1 RM strength increases in the squat and bench press were significantly greater in the protein groups than placebo Lean mass increase was significantly greater in the protein groups than placebo
Note that only the soy treatment was excluded from analysis.
Candow, Chilibeck, et al., [40] 29 untrained older men Multi-ingredient supplement containing a protein dose of 0.3 g/kg immediately before exercise and a CHO-based placebo immediately after, or the reverse order of the latter, or placebo before & after exercise No Air-displacement plethysmography, ultrasound Progressive resistance training consisting of exercises for all major muscle groups performed 3 days/wk for 12 wks 1 RM strength increases in the leg press & bench press occurred in all groups, no significant differences between groups Lean mass and muscle thickness increased in all groups, no significant difference between groups
Cribb and Hayes, [16] 23 young recreational male bodybuilders 1 g/kg of a supplement containing 40 g whey isolate, 43 g glucose, and 7 g creatine monohydrate consumed either immediately before and after exercise or in the early morning and late evening Yes DXA and muscle biopsy Progressive resistance training consisting of exercises for all major muscle groups performed 3 days/wk for 10 wks Immediate pre-post supplementation caused greater increases in 1-RM in 2 out of 3 exercises Significant increases in lean body mass and muscle CSA of type II fibers in immediate vs. delayed supplementation
Hartman et al., [41] 56 untrained young men 17.5 g protein within milk or a soy beverage, or CHO control immediately after exercise and again 1 hr after exercise No DXA and muscle biopsy Progressive resistance training consisting of exercises for all major muscle groups performed 5 days/wk for 12 wks All groups experienced 1RM strength gains, but no between-group differences were seen Type II muscle fiber area increased in all groups, but with greater increases in the milk group than in the soy and control groups, fat-free mass increased to a greater extent in the milk group compared to the soy & control groups
Note that only the soy treatment was excluded from analysis.
Hoffman et al., [42] 21 well-trained young men 42 g protein within a multi-ingredient supplement or a CHO placebo taken once in the morning and again after training No DXA Progressive, periodized resistance training consisting of exercises for all major muscle groups performed 4 days/wk for 12 wks 1 RM bench press strength (but not squat strength) significantly increased in the protein group, while no measures of strength increased in the placebo group No significant between-group or absolute changes in body composition occurred
Willoughby et al., [17] 19 untrained young men 20 g whey-dominant protein or 20 g dextrose consumed 1 hour before and after exercise No Hydrostatic weighing, muscle biopsy, surface measurements Progressive resistance training consisting of exercise for all major muscle groups performed 4 days/wk for 10 wks Protein supplementation caused greater increases in relative strength (maximal strength corrected for bodyweight) in bench press & leg press Significant increase in total body mass, fat-free mass, and thigh mass with protein vs. carb supplementation
Eliot et al., [43] 42 untrained older men 35 g whey protein + CHO-electrolyte solution, or whey/CHO + 5 g creatine, or creatine-only, or CHO placebo No DXA and bioelectrical impedance Progressive resistance training consisting of exercise for all major muscle groups performed 3 days/wk for 14 wks Not measured No significant effects of any of the whey and/or creatine treatments were seen beyond body composition changes caused by training alone
Note that creatine treatments were excluded from analysis
Mielke et al., [44] 39 untrained young men 20 g whey protein + 6.2 g of leucine or 20 g maltodextrin 30 minutes before and immediately after exercise No Hydrodensitometry, Dynamic constant external resistance (DCER) bilateral leg extension and bench press exercises were performed 3 days/wk for 8 wks. 1 RM strength increased significantly in both groups without any between-group differences No significant training-induced changes in body composition in either group,
Verdijk et al., [21] 28 untrained elderly men 10 g casein hydrolysate or placebo consumed immediately before and after exercise No DXA, CT, and muscle biopsy Progressive resistance training consisting leg press and knee extension performed 3 days/wk for 12 wks 1 RM leg press & leg extension strength increased, with no significant difference between groups No significant differences in muscle CSA increase between groups
Hoffman et al., [20] 33 well-trained young men Supplement containing 42 g protein (milk/collagen blend) and 2 g carbohydrate consumed either immediately before and after exercise or in the early morning and late evening Yes DXA Progressive resistance training consisting exercises for the major muscle groups peformed 4 days/wk for 10 wks. 1 RM & 5 RM bench press & squat strength increased, with no significant difference between groups No significant differences in total body mass or lean body mass between groups.
Hulmi et al., [18] 31 untrained young men 15 g whey isolate or placebo consumed immediately before and after exercise No MRI, muscle biopsy Progressive, periodized total body resistance training consisting of exercises for all major muscle groups trained performed 2 days/wk for 21 wks Strength increased similarly in the protein & placebo group, but only the protein group increased isometric leg extension strength vs the control group Significant increase in CSA of the vastus lateralis but not of the other quadriceps muscles in the protein group vs placebo
Josse et al., [45] 20 untrained young women 18 g protein within milk or an isocaloric maltodextrin placebo immediately after exercise and again 1 hr later No DXA Progressive, periodized resistance training consisting of exercises for all major muscle groups performed 5 days/wk for 12 wks 1 RM strength increased similarly in both groups, but milk significantly outperformed placebo in the bench press Lean mass increased in both groups but to a significantly greater degree in the milk group, fat mass decreased in the milk group only
Walker et al., [46] 30 moderately trained men and women 19.7 g of whey protein and 6.2 g leucine or isocaloric CHO placebo 30–45 minutes before exercising and the second packet 30–45 minutes after exercising. No DXA Bodyweight-based exercises and running at least 3 days/wk, externally loaded training not specified 1 RM bench press strength increased significantly in the protein group only Total mass, fat-free mass, and lean body mass increased significantly in the protein group only
Vieillevoye et al., [47] 29 untrained young men 15 g EAA + 15 g saccharose. or 30 g saccharose consumed with breakfast and immediately after exercise No Ultrasonography, 3-site skinfold assessment with calipers, 3-site circumference measurements Progressive, periodized resistance training consisting of exercises for all major muscle groups performed 2 days/wk for 12 wks Maximal strength significantly increased in both groups, with no between-group diffrerence Muscle mass significantly increased in both groups with no differences between groups, muscle thickness of the gastrocnemius medialis significantly increased in the EAA group only
Wycherly et al., [22] 34 untrained, older men & women w/type 2 diabetes 21 g protein, 0.7 g fat, 29.6 g carbohydrate consumed either immediately prior to, or at least 2 h following exercise Yes DXA, waist circumference Progressive resistance training consisting of exercises for all major muscle groups performed 3 days/wk for 16 wks Not measured Fat mass, fat-free mass, and waist circumference decreased with no significant differences between groups
Erskine et al., [48] 33 untrained young men 20 g whey protein or placebo consumed immediately before and after exercise No MRI 4-6 sets of elbow flexion performed 3 days/wk for 12 weeks No significant differences in maximal isometric voluntary force or 1 RM strength between groups No significant differences in muscle CSA between groups
Weisgarber et al., [49] 17 untrained young men and women Whey protein dosed at 0.3 g/kg or isocaloric CHO immediately before, during, and after exercise No DXA and ultrasound Progressive resistance training consisting of exercises for all major muscle groups performed 4 days/wk for 8 wks 1 RM strength in the chest press increased in both groups without any between-group difference Significant increases in muscle mass were seen without any difference between groups