Table 1 Characteristics and main outcomes of the included studies

Akagi and Takahashi [42]

RCT

19

19

-

Unilateral design

23.7 ± 2.3

Sedentary or recreationally active participants

 TH

A 5-week unilateral stretching intervention decreased gastrocnemius muscle hardness but did not change muscle thickness and the ratio of GM hardness to GL hardness

Andrade et al. [9]

RCT

39

19

20

21

18

21.0 ± 2.4

21.1 ± 2.0

Physical education & sport science university students

FL, TH

Compared with the control group, muscle directed static stretching for 12 weeks, showed increased ROM, decreased shear wave velocity of triceps surae, decreased passive torque and greater GM fascicle length. There were no significant changes in GL fascicle length and in GM and GL thickness

Blazevich et al. [24]

RCT

24

24

-

15

9

18.6 ± 0.9

18.6 ± 0.9

NR

FL

A 3-week stretching training increased dorsiflexion ROM and passive joint moment at end ROM in the stretched compared with the control group. Muscle and fascicle strain increased along with a decrease in muscle stiffness during stretch to a constant joint angle. Muscle length at end ROM increased without a change in fascicle length, fascicle rotation, tendon elongation and tendon stiffness, following training. No change in maximum voluntary contraction moment and rate of force development at any joint angle was observed

Brusco et al. [41]

CT

10

10

-

Unilateral design

24.4 ± 4.1

Untrained participants

 TH

After 6 weeks of unilateral static stretching, hip ROM increased only in the experimental leg. Biceps femoris thickness was significantly inreased at all time points and semitendinous thickness and echo intensity significantly increased at 72 h post stretching. However, no significant differences were found between the stretched and the control leg

Freitas and Mil-Homens [23]

RCT

10

10

-

5

5

21.2 ± 0.8

21.2 ± 0.8

University students

FL, PA, TH

An 8-week stretching intervention significantly increased BF fascicle length and hip joint ROM in the stretching compared with the control group. No changes were found in BF muscle thickness and pennation angle

Kay et al. [21]

RCT

26

16

10

13

13

27.8 ± 8.0

27.8 ± 8.0

Recreationally active participants

FL, PA, TH

After a 6-week active stretch training program, significant increases were found in eccentric and isometric moments, stretch tolerance, elastic energy storage, VL thickness, pennation angle and tendon stiffness. No change was observed in VL resting fascicle length and VL passive muscle–tendon stiffness

Konrad and Tilp [26]

RCT

49

35

14

25

24

23.3 ± 3.1

22.9 ± 2.4

Police Cadets

FL, PA

Following 6 weeks of static stretching, ankle ROM increased in the intervention group compared with the control. However, GM fascicle length, pennation angle, muscle stiffness and tendon stiffness remained unaltered post-intervention

Lima et al. [43]

RCT

23

23

-

12

11

19.1 ± 1.4

9.0 ± 0.2

Physically active participants

FL, PA, TH

After 8 weeks of stretching no significant changes were observed in VL and BF muscle architecture, extension torque and knee flexion angle. However, knee extension angle increased significantly in the experimental compared with the control group

Longo et al. [16]

RCT

30

18

12

15

15

22.3 ± 0.8

23.4 ± 0.8

Recreationally active participants

FL, PA, TH

Compared to pre-intervention, a static stretching intervention of 12-weeks increased ankle ROM in the intervention group while muscle tendon complex stiffness decreased. No changes were found in triceps surae architecture (FL, PA, TH), and plantar flexors force generating capacity. No changes occurred in the control group in any variable

Mizuno [20]

CT

24

15

9

12

12

18.5 ± 0.7

18.8 ± 0.7

University students

PA, TH

A static stretching intervention of 8 weeks significantly increased ankle ROM and GM muscle thickness in the stretching compared with the control group. In addition, there were significant increases in plantar flexion one-repetition maximum strength and pennation angle in the stretching and the control group

Moltubakk et al. [17]

RCT

26

9

17

Unilateral design

22.0 ± 1.6

Recreationally active university students

 FL, PA, THFL, PA, TH

Following 24 weeks of static stretching, ankle ROM increased and passive torque and normalized EMG amplitude at a standardized dorsiflexion decreased. Increases were seen in passive tendon elongation at a standardized force and in maximal passive muscle and tendon elongation. No changes were seen in tendon stiffness, resting tendon length or GM fascicle length. No changes were found in GM thickness and pennation angle in the stretched leg

Nakamura et al. [22]

RCT

40

40

-

14

13

21.4 ± 1.0

21.9 ± 1.3

University students

FL, PA, TH

High-intensity stretching improved ankle ROM and decreased muscle stiffness more than low intensity stretching. No significant changes were observed for muscle strength, drop jump height, and muscle architecture (FL, PA, TH) in both stretching groups compared to controls

13

21.4 ± 1.1

University students

Nakamura et al. [25]

RCT

18

18

-

9

9

21.1 ± 2.3

21.8 ± 0.8

NR

FL

Following 4 weeks of stretching, ankle ROM and gastrocnemius medialis MTJ displacement significantly increased while passive torque at 30° significantly decreased in the stretching compared with the control group. No increase was found in GM fascicle length in the stretching group

Panidi et al. [15]

RCT

21

–

21

Unilateral design

13.5 ± 1.4

Volleyball athletes

FL, PA, TH, ACSA

Following 12 weeks of stretching, ankle dorsiflexion increased in both legs with a greater increase in the stretched compared with the control leg. Fascicle length in the middle part of GM at rest and during stretching and fascicle length in the distal part of GL during stretching, increased only in the stretched leg. No changes were found in GM and GL penation angle and thickness. A greater increase was found in CSA and in one-leg jumping height in the stretched compared with the control leg

Peixinho et al. [37]

RCT

20

20

–

12

8

18.9 ± 0.5

Physically active

FL, PA, ACSA

Following 10 weeks of static stretching training maximum dorsiflexion, peak passive torque, and muscle–tendon unit maximum length significantly increased. No other differences were found related to muscle architecture

Şekir et al. [44]

CT

23

23

-

12

11

23.1 ± 3.1

22.2 ± 2.9

Recreational level athletes

FL, PA, TH

Following a 6-week stretching intervention, no significant increases were found for peroneal and tibial muscles architecture (FL, PA, TH)

Simpson et al. [14]

CT

22

11

11

Unilateral design

22.0 ± 2.0

NR

FL, PA, TH

After 6 weeks of overloaded static stretching gastrocnemius muscle thickness increased by 5.6%. Overall fascicles lengthened by 25% in the muscle tendon junction and 5.1% in the muscle belly. The fascicles in GL lengthened to a greater extent than in GM. Pennation angles remained unaltered in GM but decreased in GL. No change was observed in maximm voluntary contraction, voluntary activation, tendon length or thickness

Warneke et al. [45]

CT

27

16

11

Unilateral design

27.4 ± 3.1

26.8 ± 3.9

Athletically active subjects

TH

After a 6 weeks static stretching intervention using an orthosis, maximal isometric strength, 1RM and ROM significantly increased. In addition, there was a significant contralateral transfer in maximal strength. A significant increase was observed in muscle thickness in the GL of the stretched leg

Yahata et al. [18]

CT

16

16

-

Unilateral design

21.4 ± 1.5

NR

FL, PA, TH

After a 5 week stretching intervention, significant increases were found in maximum voluntary isometric contraction, at neutral ankle position. No changes were found in muscle architecture (FL, PA, TH) for both the intervention and the control legs

Participants total

467

342

125