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Table 4 Nitrate meta-analysis and sub-group analyses

From: Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials

  k n SMD (95% CIs) p I2 (%)
Overall 81 956 0.15 [0.12, 0.18] <0.001 6.4
Design    Qb: 2.37 0.121  
Crossover 76 856 0.14 [0.11, 0.17] <0.001 0
Parallel 5 100 0.36 [0.08, 0.64] 0.011 32
Blinding    Qb: 1.29 0.544  
Single blind 8 77 0.11 [-0.002, 0.22] 0.054 0
Double blind 71 857 0.16 [0.12, 0.19] <0.001 0
Unclear 2 22 0.07 [-0.14, 0.29] 0.519 60
Supplementation duration    Qb: 3.05 0.084  
Acute 38 437 0.12 [0.06, 0.17] <0.001 13
Multiple days 43 519 0.18 [0.13, 0.22] <0.001 9
Sex1    Qb: 6.94 0.031  
Male 59 658 0.16 [0.12, 0.20] <0.001 0
Female 4 48 0.0 [-0.12, 0.11] 0.988 0
Mixed 16 229 0.15 [0.09, 0.21] <0.001 0
Performance level    Qb: 8.78 0.032  
PL12 1 14 -0.29 [-0.69, 0.11] 0.156 -
PL2 23 290 0.24 [0.12, 0.35] <0.001 52
PL2 females -     
PL2 males: 17 181 0.24 [0.11, 0.36] <0.001 52
GXT 3 34 0.16 [-0.14, 0.46] 0.300 80
IGXT 1 14 0.22 [0.01, 0.44] 0.040  
ITTE 1 12 0.47 [0.03, 0.91] 0.038  
TT 4 47 0.01 [-0.28, 0.29] 0.975 53
TTE 8 74 0.39 [0.21, 0.57] <0.001 27
PL3 15 154 0.18 [0.12, 0.24] <0.001 0
PL3 females -     
PL3 males: 15 154 0.18 [0.12, 0.24] <0.001 0
GXT 2 17 0.1 [-0.27, 0.47] 0.612 53
ITT 2 20 0.17 [0, 0.35] 0.592 0
TT 8 82 0.17 [0.1, 0.24] <0.001 0
TTE 3 35 0.26 [-0.18, 0.69] 0.249 71
PL4 8 87 0.03 [-0.14, 0.2] 0.762 0
PL4 females 1 14 0.02 [-0.37, 0.42] 0.912 -
PL4 males: 7 73 0.03 [-0.16, 0.22] 0.787 0
GXT 1 12 2.17 [-1.8, 6.14] 0.289 -
TT 6 61 0.02 [-0.17, 0.22] 0.825 0
PL5 6 57 -0.02 [-0.22, 0.17] 0.821 0
PL5 females 1 12 -0.01 [-0.43, 0.42] 0.980 -
PL5 males: 5 45 -0.03 [-0.25, 0.19] 0.808 0
ITTE 1 9 -0.07 [-0.56, 0.42] 0.801 -
TT 4 36 -0.02 [-0.27, 0.23] 0.882 0
Exercise mode    Qb: 2.29 0.825  
Cycling 53 625 0.17 [0.12, 0.22] <0.001 22
Hand cycling 4 39 0.02 [-0.21, 0.26] 0.859 0
Incline walk/run 1 14 -0.29 [-0.69, 0.11] 0.156 -
Kayaking 2 14 0.13 [-0.02, 0.28] 0.093 0
Rowing 2 20 0.09 [-0.24, 0.42] 0.604 0
Running 15 196 0.14 [0.07, 0.21] <0.001 19
Swimming 4 48 0.12 [0.004, 0.23] 0.042 0
Test type    Qb: 10.29 0.059  
GXT 15 176 0.15 [0.02, 0.27] 0.023 59
IGXT 2 50 0.13 [0.03, 0.22] 0.008 0
ITT 4 44 0.13 [0.002, 0.27] 0.046 0
ITTE 2 21 0.21 [-0.02, 0.39] 0.244 60
TT 39 436 0.12 [0.07, 0.16] <0.001 0
TTE 19 229 0.31 [0.20, 0.42] <0.001 29
Test duration    Qb: 2.89 0.577  
<5 mins: 11 104 0.16 [0.08, 0.23] <0.001 0
TT 8 70 0.12 [0.04, 0.21] 0.005 0
TTE 3 34 0.32 [0.07, 0.56] 0.011 29
5-10 mins: 24 276 0.18 [0.09, 0.27] <0.001 31
TT 11 112 0.12 [0.02, 0.22] 0.016 7
TTE 13 164 0.29 [0.13, 0.44] <0.001 40
10-30 mins: 12 122 0.16 [0.04, 0.28] 0.007 41
TT 9 91 0.12 [-0.004, 0.23] 0.058 41
TTE 3 31 0.44 [0.16, 0.73] 0.002 0
30-60 mins: 5 60 0.08 [-0.11, 0.28] 0.397 0
TT 5 60 0.08 [-0.11, 0.28] 0.397 0
>60 mins: 4 51 0.00 [-0.21, 0.21] 0.986 0
TT 4 51 0.00 [-0.21, 0.21] 0.986 0
Overall (TT & TTE) 56 613 0.15 [0.11, 0.19] <0.001 2
  1. 1 Sex not specified in two trials. Abbreviations – GXT, graded exercise test; IGXT, intermittent graded exercise test; ITT, intermittent time-trial; ITTE, intermittent time to exhaustion; k, number of trials; LCI, lower confidence interval; n, pooled sample size; PL, performance level; Qb, between-group Q-statistic; SMD, standardised mean difference (Hedge’s g); TT, time-trial; TTE, time to exhaustion; UCI, upper confidence interval