Table 2 Summary of the characteristics of the included studies

Number of studies

59

24

82

Number of participants

2440

1500

3940

Age (years)

45.5

72.1

55.6

 Number of participants aged 19–59

1461

81

1542

 Number of participants aged 60–87

923

1389

2312

Sex (men %)

62

38

53

Race (Caucasian %)

88

63

78

Height (cm)

171

164

168

 Number of participants (149–169 cm)

768

1022

1790

 Number of participants (170–185 cm)

1460

329

1789

Body weight (kg)

78.8

68.1

74.8

 Number of participants (46–74 kg)

672

977

1649

 Number of participants (75–102 kg)

1631

395

2026

Body mass index (kg/m²)

26.6

25.4

26.1

 Number of participants (20.6–24.9 kg/m²)

768

516

1284

 Number of participants (25.0–37.9 kg/m²)

1597

963

2560

Energy intake (kcal/day)

2141

1752

2035

 Number of participants (1298–1999 kcal/day)

561

418

979

 Number of participants (2000–3539 kcal/day)

819

100

919

Baseline protein intake (g/kg BW/d)

0.39

0.37

0.38

 Number of participants (0.60–0.99 g/kg BW/d)

561

314

875

 Number of participants (1.00–2.10 g/kg BW/d)

1235

962

2197

Added protein intake (g/kg BW/d) (intervention groups)

0.39

0.37

0.38

 Number of participants (0.04–0.49 g/kgBW/d)

1036

582

1618

 Number of participants (0.50–2.06 g/kgBW/d)

274

212

486

Total protein intake (g/kg BW/d) (intervention groups)

1.50

1.46

1.49

 Number of participants (0.79–1.49 g/kgBW/d)

708

393

1101

 Number of participants (1.50–3.80 g/kgBW/d)

472

311

783

Trial periods (weeks)

15.1

33.3

22.0

 Number of participants (3 weeks to 2.9 months)

1845

719

2564

 Number of participants (3 months to 2 years)

595

781

1376

Habitual training (%)

13

0

8

Body part

 Upper body (%)

64

83

72

 Lower body (%)

78

57

70

Contraction type

 Isokinetic (%)

15

14

15

 Isometric (%)

37

96

59

 Isotonic (%)

82

13

55