Table 1 Characteristics and main outcomes of the included studies

Azuma and Someya [48]

RCT

124

124

–

64

60

16.2 ± 0.8

16.2 ± 0.8

Soccer

3240

No pain

0.74–1.51

The SG showed significant higher values in heel–buttock distance, straight leg raise, hip rotation angles, and ankle dorsiflexion at 12 weeks relative to pre-intervention values. Positive effects were also found in injury rate. No increases were observed in the CG

Beccera-Fernadez et al. [49]

RCT

102

102

49

53

16–17

16–17

Students

1920

Stretch position was held gently

0.27

A physical education-based program for eight weeks significantly improved students’ hamstrings extensibility in the SG compared to the CG

Coledam et al. [29]

CT

58

29

29

14

15

8.6 ± 0.7

8.5 ± 0.5

Students

3840

NR

0.88 (boys)

Performance of stretching exercises during warm-up for 16 weeks significantly improved sit and reach score in the SG compared to the CG

14

15

8.4 ± 0.5

8.6 ± 0.7

Students

1.26 (girls)

de Baranda [50]

RCT

50

23

27

26

24

13.7 ± 0.4

13.7 ± 0.4

Students

16,740

NR

1.30–1.47

Significant improvements were found in straight leg raise in the SG compared with the CG after 31 weeks of stretching training

Donti et al. [43]

CT

77

–

77

57

20

9.3 ± 0.8

8.9 ± 0.6

Gymnasts

4050

POD

2.27 (intermittent stretching)

0.91 (continuous stretching)

ROM increased following an intermittent or a continuous static stretching program of 12 weeks in youth female gymnasts but remained unchanged in the control group. Intermittent stretching conferred a larger improvement compared to continuous

Donti et al. [44]

CT

30

–

30

19

11

9.8 ± 0.5

9.5 ± 0.8

Gymnasts

2430

POD

0.92 (intermittent stretching)

0.60 (continuous stretching)

Hip hyperextension ROM increased similarly following an intermittent or a continuous stretching protocol of 9 weeks. No increase in ROM was observed in the CG. Counter movement jump height after stretching was not affected by either stretching protocol

Hadjicharalambous [51]

RCT

23

23

11

12

16.1 ± 0.7

16.0 ± 0.6

Soccer

6144

Point of mild discomfort

1.48

Flexibility training for four weeks improved sit and reach score, 35 m sprint, agility and broad jump in adolescent soccer players more than soccer training alone

Hill and Najera [45]

CT

102

53

49

60

42

13–15

13–15

Students

3240

Tightness/no pain

0.60

A significant improvement was observed in the SG compared to CG in hamstring extensibility following 9 weeks of stretching in a physical education setting

Kamandulis et al. [52]

CT

229

107

122

62

58

15.1 ± 0.3

15.2 ± 0.5

200

800

3200

0.24 (boys)

0.18 (girls)

Static stretching performed once, four times, or in a set of four exercises repeated four times during physical education classes increased ROM in adolescent students; however, the higher volume stretching protocol induced greater improvements in ROM. No improvement was observed in the CG

55

15.0 ± 0.4

Students

200

800

3200

NR

0.40 (boys)

0.58 (girls)

54

15.0 ± 0.4

200

800

3200

0.60 (boys)

0.81 (girls)

Knapik et al. [53]

RCT

106

46

60

51

55

15.8 ± 1.3

16.3 ± 1.0

Basketball

50,400

NR

0.25 (boys)

0.53 (girls)

Athletes undergoing gastrocnemius stretching demonstrated significant increases in ankle dorsiflexion following 3 months of training and greater ankle dorsiflexion compared with controls at all time points

Mayorga-Vega et al. [57]

RCT

73

36

37

25

24

9.0 ± 0.2

9.0 ± 0.2

Students

3600

Gentle feeling of tightness

Gentle feeling of tightness

0.09 (warm-up)

0.11 (cool down)

Students performing stretching either during warm-up or cool down for ten weeks had higher values in hamstrings extensibility than no-training students. No difference was observed between warm-up and cool down groups

24

9.0 ± 0.2

Students

3600

Mayorga-Vega et al. [58]

RCT

45

24

21

22

23

9.9 ± 0.3

9.9 ± 0.3

Students

3840

Tightness/no pain

0.28

A short-term (5 weeks) stretching intervention increased sit and reach score in elementary school children. No increase was observed in the CG

Mayorga Vega et al. [59]

RCT

45

26

19

22

23

10.9 ± 0.3

10.9 ± 0.3

Students

4800

Tightness/no pain

0.34

A stretching intervention during physical education classes significantly increased hamstring and lumbar extensibility in the SG compared to the CG

Mayorga-Vega et al. [54]

RCT

163

84

79

53

58

12.7 ± 0.7

12.6 ± 0.6

Students

1920

Tightness/no pain

0.23

Stretching performed once or twice a week during physical education class improved hamstrings extensibility in the two SG compared to CG. No differences were observed between the two SG

52

12.7 ± 0.6

Students

3840

0.24

Mayorga-Vega et al. [56]

RCT

89

43

46

44

45

8.5 ± 0.8

8.4 ± 0.6

Students

4320

Tightness/no pain

0.47

A physical education-based stretching intervention for 9 weeks improved more hamstrings extensibility in the SG compared to the CG

Mayorga-Vega et al. [55]

RCT

37

18

19

19

18

9.0

9.0

Students

5040

Tightness/no pain

0.71

A physical education stretching program for 34 weeks increased sit and reach score in the SG compared to the CG

Merino-Marban et al. [61]

RCT

45

26

19

23

22

5.9 ± 0.3

5.9 ± 0.3

Students

960

Tightness/no pain

0.45

An 8-week stretching intervention significantly increased the sit and reach score in the SG compared to the CG

Moreira et al. [62]

RCT

58

30

28

28

30

12.2 ± 1.8

11.9 ± 2.1

Students

360

Stretching as much as tolerable

0.52

A six weeks stretching program improved hamstrings extensibility in secondary school children. No improvement was observed in the CG

Nelson and Bandy [63]

RCT

45

45

–

21

24

16.2 ± 1.1

16.5 ± 1.0

Students

540

Gentle feeling of stretch

1.72

Six weeks of static stretching increased hamstrings extensibility in adolescent males compared to controls

Panidi et al. [64]

RCT

21

–

21

21

21

13.5 ± 1.4

13.5 ± 1.4

Volleyball

45,900

POD

3.48

High-volume static stretching of the plantar flexors was applied for 12 weeks to one leg with the contralateral leg as control. Ankle dorsiflexion increased in both legs with a greater increase in the stretched compared to control leg. A greater increase was also observed in jumping height in the stretched compared to the control leg

Piqueras-Rodríguez et al. [65]

RCT

42

42

–

21

21

12.3 ± 1.6

12.3 ± 1.8

Soccer

720

Tolerable stretch

0.17–0.99

Stretching increased straight leg raise, toe-touch and passive knee extension scores in the SG compared to CG after 8 weeks of training

Reid and McNair [68]

RCT

43

43

–

23

20

15.8 ± 1.1

15.7 ± 0.9

Students

2700

NR

1.45

Stretching intervention induced significant increases in passive knee extension range of motion, passive resistive force and stiffness in the SG while no differences were observed in the CG

Rodríguez et al. [66]

RCT

46

20

26

25

21

10.3 ± 0.3

10.3 ± 0.3

Students

19,200

Gentle feeling of stretch

0.28

Five minutes of stretching during physical education classes for a period of 32 weeks, significantly increased sit and reach score in elementary school children whereas the score decreased in the CG

44

21

23

24

20

13.5 ± 0.7

13.5 ± 0.7

Students

19,200

0.93

Sánchez Rivas et al. [67]

RCT

44

20

24

22

22

7.9 ± 0.4

7.9 ± 0.4

Students

3240

POD

0.30

A three-minute static passive hamstrings stretching program over nine weeks improved sit and reach score in the SG compared to CG

Santonja Medina et al. [60]

CT

63

NR

NR

25

18

10.3 ± 0.5

10.3 ± 0.3

Students

4960

Gentle feeling of stretch

0.90 (left leg)

0.93 (right leg)

Significant improvements in ROM were observed after a school term (9 months) of flexibility training in the two experimental groups compared to the control group that followed a standard physical education class

20

10.5 ± 0.6

Students

9920

1.68 (left leg)

2.10 (right leg)

Sermaxhaj et al. [46]

CT

24

24

–

12

12

13.8 ± 0.5

14.0 ± 0.4

Soccer

10,560

NR

0.40

Static stretching performed at the end of the training session for 4 months did not increase sit and reach score in the SG compared to the CG

Sermaxhaj et al. [47]

CT

68

68

10

10

12.0 ± 0.4

11.9 ± 0.5

8640

0.60

Following 16 weeks of stretching, only the SG of the cadet football players (15–17 years old) improved their sit and reach score compared with the CG

12

12

13.8 ± 0.5

14.0 ± 0.4

Football

8640

Further possible bend

0.40

12

12

15.9 ± 0.6

15.6 ± 0.4

8640

0.60

Vans Rensburg and Coetzee [69]

RCT

40

40

20

20

13–17

13–17

Students

2700

Point of tightness

2.74

After six weeks of static stretching, hamstrings extensibility increased in the SG compared with the CG

All Participants (n)

1936

975

898

Participants ≤ 11 years (n)

652

242

347

Participants ≥ 12 years (n)

1284

703

523