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Table 3 Subgroup analyses of the effects of protein intake on muscle strength

From: Synergistic Effect of Increased Total Protein Intake and Strength Training on Muscle Strength: A Dose-Response Meta-analysis of Randomized Controlled Trials

  RT Non-RT All
  N/study MD (95% CI) (%) I2 (%) N/study MD (95% CI) (%) I2 (%) N/study MD (95% CI) (%) I2 (%)
All 2440/59 2.01 (1.09, 2.93) 16 1500/24 0.13 (− 1.53, 1.79) 49 3940/82 1.40 (0.55, 2.24) 32
Subgroup analysis
Age (years)
 < 60 1461/37 2.35 (1.00, 3.69) 27 81/2 0.95 (− 4.97, 6.86) 46 1542/39 2.25 (0.95, 3.54) 27
 ≥ 60 923/22 1.38 (0.39, 2.36) 0 1389/21 0.20 (− 1.65, 2.04) 53 2312/42 0.64 (− 0.47, 1.75) 35
Sex
 Female 403/13 1.54 (0.46, 2.62) 0 292/5 2.48 (− 5.43, 10.39) 74 695/18 1.38 (− 0.28, 3.04) 28
 Male 1078/33 2.07 (0.71, 3.43) 9 105/3 − 0.95 (− 3.51, 1.60) 0 1183/35 1.64 (0.37, 2.91) 13
Baseline protein intake (g/kg BW/d)
 < 1.0 561/12 1.46 (0.45, 2.48) 0 314/6 − 0.26 (− 2.56, 2.03) 20 875/18 1.06 (− 0.01, 2.13) 11
 ≥ 1.0 1235/31 2.11 (0.76, 3.46) 0 962/13 − 0.81 (− 3.00, 1.38) 51 2197/43 0.93 (− 0.35, 2.21) 32
Added protein intake (g/kg BW/d)b
  < 0.5 1849/45 1.22 (0.41, 2.03) 0 1056/18 1.38 (− 0.95, 3.71) 57 2905/63 1.10 (0.17, 2.03) 22
 ≥ 0.5 538/14 4.29 (1.99, 6.60) 40 356/6 − 1.64 (− 3.52, 0.25) 0 894/19 2.36 (0.35, 4.37) 55
Trial periods (months)a
 < 3 1845/50 2.27 (1.23, 3.30) 19 719/15 0.95 (− 1.56, 3.46) 53 2564/64 1.90 (0.91, 2.90) 31
 ≥ 3 595/9 0.66 (− 1.22, 2.54) 0 781/9 − 0.67 (− 2.84, 1.50) 44 1376/18 − 0.05 (− 1.52, 1.43) 26
Contraction type
 Isokinetic 370/7 0.71 (− 4.69, 6.11) 59 217/3 − 1.11 (− 5.25, 3.03) 45 587/10 − 0.03 (− 3.53, 3.47) 54
 Isometric 892/18 0.92 (− 0.33, 2.17) 7 1439/22 0.26 (− 1.70, 2.23) 60 2331/39 0.33 (− 0.91, 1.56) 47
 Isotonic 1989/49 2.30 (1.25, 3.36) 21 191/6 0.57 (− 1.99, 3.13) 0 2180/54 2.13 (1.16, 3.11) 19
Body part
 Upper body 1570/44 1.39 (0.25, 2.54) 52 1252/20 0.15 (− 1.65, 1.95) 59 2822/63 0.99 (0.01, 1.98) 56
 Lower body 1898/50 2.77 (1.46, 4.07) 39 853/15 0.40 (− 1.82, 2.62) 24 2751/64 2.21 (1.07, 3.34) 38
  1. RT resistance training, MD mean difference, BW body weight
  2. aStatistically significant difference subgroups in the analysis of all trials (P < 0.05)
  3. bStatistically significant difference subgroups in the analysis of trials with RT (P < 0.05)