Key points
-
Tendons are highly responsive to increased mechanical loading and adapt through changes of their mechanical, material, and morphological properties.
-
Changes in tendon stiffness seem to be more attributed to adaptations of the material rather than morphological properties.
-
An effective training intervention for the tendon should apply a high loading intensity over a longer intervention duration (>12 weeks).
Background
Methods
Search strategy
Study selection and inclusion criteria
Methodological quality and risk of bias
Scoring
| |
---|---|
Internal validity
| |
1. Study design | A positive point was assigned if the following aspects were considered: |
1. Mechanical tendon properties (stiffness) | |
2. Material tendon properties (Young’s modulus) | |
3. Morphological tendon properties (cross-sectional area) | |
4. Control group (no specific training) was included and participants were randomly assigned | |
2. Methods | A positive point was assigned if the following aspects were considered: |
2.1 Mechanical properties | |
• Object of investigation | A. Only the free tendon was assessed [79] |
• Calculation of tendon force | |
E. Tendon lever arm directly measured for each subject | |
• Measurement of tendon elongation | |
G. Using the average of multiple trials (>1) to increase the reliability of the ultrasound technique [86] | |
2.2 Morphological properties | |
3. Cofactors | A positive point was assigned if the following aspects were considered: |
A. Influence of gender | |
B. Influence of physical activity level of the participants | |
Statistical validity
| |
4. Statistical tests | A positive point was assigned if appropriate statistical tests were used |
5. Power analysis | A positive point was assigned if effect sizes were calculated and reported |
External validity
| |
6. Eligibility of sample and variable | A positive point was assigned if the intervention included: |
1. Appropriate participant sample | |
2. Appropriate variables | |
7. Description of the exercise intervention protocol | A positive point was assigned if the following criteria were reported: |
A. Intensity of muscle contraction | |
B. Duration of single stimulus | |
C. Repetitions per set | |
D. Number of sets | |
E. Number of weeks of intervention | |
F. Number of trainings per week | |
8. Description of the participant sample | A positive point was assigned if the following criteria were reported: |
A Age, B Gender, C Body height, D Body weight, E Activity level |
Data extraction
Statistical analysis
Results
Literature search
Description of the included studies
Source
|
Participants
|
Intervention
|
Outcome
| ||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Reference
|
Year
|
Group
|
N
|
Sex
|
Activity level
|
Tendon
|
Type of training
|
Intensity
|
Duration
|
Reps
|
Sets
|
Weeks
|
Times/week
|
Stiffness
|
YM
|
CSA
| |||||
Location
|
%
|
Sig
|
%
|
Sig
|
Location
|
%
|
Sig
| ||||||||||||||
Albracht et al. [15] | 2013 | EP | 13 | m | Run | AT | Is (rep) | 90% MVC | 3 s | 4 | 5 | 14 | 4 | Ap (GM F) | 15.8 | * | |||||
Arampatzis et al. [29] | 2010 | EP | 11 | m | Reg | AT | Is (rep) | 55% MVC | 1 s | 20 | 5 | 14 | 4 | Ap (GM F) | −5.2 | - | −4.8 | - | Free | 1.3 | - |
EP | 11 | m | Reg | AT | Is (rep) | 90% MVC | 1 s | 12 | 5 | 14 | 4 | Ap (GM F) | 17.1 | * | 16.9 | * | Free | 0.5 | - | ||
Arampatzis et al. [28] | 2007 | EP | 11 | f, m | Reg | AT | Is (rep) | 55% MVC | 3 s | 7 | 5 | 14 | 4 | Ap (GM F) | 7.9 | - | −1.6 | - | Free | 4.3 | - |
EP | 11 | f, m | Reg | AT | Is (rep) | 90% MVC | 3 s | 4 | 5 | 14 | 4 | Ap (GM F) | 36.0 | * | 22.9 | * | Free | 9.6 | * | ||
Bohm et al. [31] | 2014 | EP | 12 | m | Reg | AT | Is (sta) | 90% MVC | 12 s | 1 | 5 | 14 | 4 | Ap (GM M) | 24.8 | * | 17.7 | * | Free | 5.3 | * |
EP | 12 | m | Reg | AT | Is (rep) | 90% MVC | 3 s | 4 | 5 | 14 | 4 | Ap (GM M) | 53.9 | * | 45.2 | * | Free | 4.4 | * | ||
EP | 14 | m | Reg | AT | Ply | 90% MVC | Approximately 0.26 s | 72 | 5 | 14 | 4 | Ap (GM M) | 28.4 | - | 19.6 | - | Free | 2.5 | - | ||
EP | 14 | m | Reg | AT | Is (rep) | 90% MVC | 3 s | 4 | 5 | 14 | 4 | Ap (GM M) | 37.3 | * | 36.3 | * | Free | 3.7 | * | ||
Carroll et al. [61] | 2011 | CG | 7 (11) | f, m | Unt | PT | Co-Ec (rep) | 74% RM | nr | 2 to 3 | 5 to 10 | 12 | 3 | Free | 13.9 | + | 18.4 | * | Free | −1.7 | - |
Fletcher et al. [17] | 2010 | EP | 6 | m | Run | AT | Is (sta) | 80% MVC | 20 s | 1 | 4 | 8 | 3 | Ap (GM F) | 18.6 | - | |||||
Fouré et al. [71] | 2009 | EP | 6 | m | Exp | AT | Ply | nr | nr | 150 to 280 | nr | 8 | 2 | Ap (GM M) | 4.1 | - | |||||
2010a,b,2011 | EP | 9 | m | Reg | AT | Ply | nr | nr | 200 to 600 | nr | 14 | 2.4 | Ap (GM M) | 26.5 | * | Free | 3.1 | - | |||
Foure et al. [43] | 2013 | EP | 11 | m | Reg | AT | Ec (rep) | nr | nr | 200 to 600 | nr | 14 | 2.4 | Ap (GM F) | 16.4 | - | Free | −1.5 | - | ||
Hansen et al. [62] | 2003 | EP | 11 | f, m | Unt | AT | Run | nr | 30 to 50 min | 1 | 34 | 2.4 | Ap (GM F) | 7.3 | - | Free | −0.3 | - | |||
Houghton et al. [39] | 2013 | EP | 7 | nr | Cri | AT | Ply | nr | nr | 4 to 10 | 2 to 6 | 8 | 1.9 | Ap (GM M) | −8.9 | - | −20 | - | Free | 12.9 | * |
Kongsgaard et al. [24] | 2007 | EP | 12 | m | Unt | PT | Co-Ec (rep) | 70% RM | nr | 8 | 10 | 12 | 3 | Free | 14.6 | * | 12.2 | - | Free | 3.3 | nr |
EP | 12 | m | Unt | PT | Co-Ec (rep) | 16% RM | nr | 36 | 10 | 12 | 3 | Free | −9.2 | - | −4.2 | - | Free | 1.5 | nr | ||
2001a | EP | 8 | m | Reg | PT | Is (rep) | 70% MVC | Rapid | 50 | 3 | 12 | 4 | Ap (VL F) | 17.5 | - | Free | 1.4 | - | |||
2001a,b | EP | 8 | m | Reg | PT | Is (sta) | 70% MVC | 20 s | 1 | 4 | 12 | 4 | Ap (VL F) | 57.3 | * | 50.3 | * | Free | 1.4 | - | |
Kubo et al. [25] | 2002 | EP | 8 | m | Reg | AT | Co-Ec (rep) | 70% RM | nr | 10 | 5 | 8 | 4 | Ap (GM F) | 31.3 | * | Free | −3.3 | - | ||
EP | 8 | m | Reg | AT | Co-Ec (rep) + S | 70% RM | nr + 45 s | 10 + 5 | 5 + 1 | 8 | 4 + 7 (2×/day) | Ap (GM F) | 23.8 | * | Free | 3.4 | - | ||||
Kubo et al. [63] | 2003 | EP2 | 11 | f | Reg | PT | Co-Ec (rep) | BW | nr | 44 | 1 | 24 | 6 | Ap (VL F) | 15.7 | - | |||||
Kubo et al. [40] | 2006a | EP | 9 | m | nr | PT | Is (sta) [50°] | 70% MVC | 15 s | 1 | 6 | 12 | 4 | Ap (VL F) | 9.7 | - | Free | 1.5 | - | ||
EP | 9 | m | nr | PT | Is (sta) [100°] | 70% MVC | 15 s | 1 | 6 | 12 | 4 | Ap (VL F) | 50.9 | * | Free | 1.5 | - | ||||
Kubo et al. [87] | 2006b | EP | 8 | m | Reg | PT | Is (sta) | 70% MVC | 15 s | 1 | 10 | 12 | 4 | Free | −0.2 | - | Free | 0.3 | - | ||
Kubo et al. [88] | 2006c | CG | 9 | m | nr | PT | Co-Ec (rep) | 80% RM | 4 s | 10 | 4 | 12 | 3 | Free | 8.5 | - | Free | −0.6 | - | ||
Kubo et al. [59] | 2007 | EP | 10 | m | Unt | AT | Ply | 40% RM | nr | 10 | 5 | 12 | 4 | Ap (GM M) | 19.4 | - | Free | 3.3 | - | ||
EP | 10 | m | Unt | AT | Co-Ec (rep) | 80% RM | 4 s | 10 | 5 | 12 | 4 | Ap (GM M) | 29.7 | * | Free | −1.2 | - | ||||
Kubo et al. [60] | 2009 | EP | 10 | m | nr | PT | Is (sta) | 70% MVC | 15 s | 1 | 10 | 12 | 4 | Free | 71.1 | * | Free | 4.0 | - | ||
EP | 10 | m | nr | PT | Co-Ec (rep) | 80% RM | 4 s | 10 | 5 | 12 | 4 | Free | 25.4 | - | Free | 1.3 | - | ||||
Kubo et al. [52] | 2010 | EP | 8 | m | Reg | PT | Is (sta) | 70% MVC | 15 s | 1 | 10 | 12 | 4 | Ap (VL F) | 50.9 | * | Free | 1.0 | - | ||
Kubo et al. [72] | 2012 | EP | 9 | m | Reg | AT | Is (sta) | 80% MVC | 15 s | 1 | 15 | 12 | 4 | Ap (GM M) | 51.4 | * | Free | 2.7 | - | ||
Malliaras et al. [41] | 2013 | EP | 9 | m | Reg | PT | Co (rep) | 80% RM | 5 s | 7 to 8 | 4 | 12 | 3 | Free | 49.9 | - | 52 | - | Free | 5.0 | - |
EP | 10 | m | Reg | PT | Ec (rep) | 80% RM | 5 s | 12 to 15 | 4 | 12 | 3 | Free | 39.2 | - | 38.6 | - | Free | 3.6 | - | ||
EP | 10 | m | Reg | PT | Ec (rep) | 80% RM (Ec) | 5 s | 7 to 8 | 4 | 12 | 3 | Free | 80.9 | * | 77.3 | * | Free | 5.8 | - | ||
Seynnes et al. [30] | 2009 | EP | 15 | m | Reg | PT | Co-Ec (rep) | 80% RM | nr | 10 | 4 | 9 | 3 | Free | 22.7 | * | 18.4 | * | Free | 3.9 | * |
Methodological quality and risk of bias assessment
Study
|
Methodological quality
|
Risk of bias
| ||||||||||||||||||||||||||||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Internal validity
|
Statistical validity
|
External validity
|
Total score [%]
|
Sequence
|
Allocation
|
Blinding
|
Outcome
|
Report
|
Other
| |||||||||||||||||||||||||||||||
1.1
a
|
1.2
a
|
1.3
a
|
1.4
a
|
2.1A
b
|
2.1B
b
|
2.1C
b
|
2.1D
b
|
2.1E
b
|
2.1F
b
|
2.1G
b
|
2.2A
b
|
2.2B
b
|
3A
b
|
3B
b
|
Score [%]
|
4
a
|
5
a
|
Score [%]
|
6.1
a
|
6.2
a
|
7A
b
|
7B
b
|
7C
b
|
7D
b
|
7E
b
|
7F
b
|
8A
b
|
8B
b
|
8C
b
|
8D
b
|
8E
b
|
Score [%]
| ||||||||
Albracht et al., 2013 [15] | + | - | - | + | - | + | + | + | - | + | - | / | / | - | + | 51 | + | - | 50 | + | + | + | + | + | + | + | + | - | + | + | + | + | 95 | 65 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Arampatzis et al., 2007 [29] | + | + | + | + | - | + | + | + | - | + | - | + | + | + | - | 87 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | - | 95 | 77 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Arampatzis et al., 2010 [28] | + | + | + | - | - | + | + | + | - | + | - | + | + | + | - | 72 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | - | 95 | 72 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Bohm et al. [31] | + | + | + | + | - | + | + | + | + | + | + | + | + | + | + | 98 | + | + | 100 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 99 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Carroll et al., 2011 [61] | + | + | + | - | + | - | - | - | - | + | + | + | + | - | + | 70 | + | - | 50 | + | + | + | - | + | + | + | + | + | + | + | + | + | 96 | 72 | Unclear’ | Unclear’ | Yes | Yes | Yes | Yes |
Fletcher et al., 2010 [17] | + | - | - | + | - | + | + | - | + | + | - | / | / | + | + | 60 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 70 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Fouré et al., 2009 [71] | + | - | - | + | - | + | - | - | - | - | - | / | / | + | + | 46 | + | - | 50 | + | + | - | - | + | - | + | + | + | + | + | + | + | 88 | 61 | Unclear | Unclear | Unclear | Unclear | Yes | Yes |
+ | - | + | + | - | + | - | - | - | + | - | - | + | + | + | 63 | + | - | 50 | + | + | - | - | + | - | + | + | + | + | + | + | + | 88 | 67 | Unclear | Unclear | Unclear | Yes | Yes | Yes | |
Foure et al., 2013 [43] | + | - | + | + | - | + | - | - | - | + | - | - | + | + | + | 63 | + | - | 50 | + | + | - | - | + | - | + | + | + | + | + | + | + | 88 | 67 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Hansen et al., 2003 [62] | + | - | + | - | - | - | - | + | + | + | - | + | + | - | + | 56 | + | - | 50 | + | + | - | + | + | + | + | + | + | + | + | + | + | 96 | 67 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Hougthon et al., 2013 [39] | + | + | + | + | - | + | + | + | + | + | - | - | + | + | + | 84 | + | + | 100 | + | + | - | - | + | + | + | + | + | + | + | + | + | 92 | 92 | Unclear | Unclear | Unclear | Yes | Yes | Unclear+
|
Kongsgaard et al., 2007 [24] | + | + | + | - | + | + | - | + | - | + | - | + | + | + | + | 74 | + | - | 50 | + | + | + | - | + | + | + | + | + | + | + | + | + | 96 | 73 | Unclear’ | Unclear’ | Yes | Yes | Yes | Yes |
+ | + | + | - | - | - | - | - | - | - | + | + | - | + | + | 66 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 72 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes | |
Kubo et al., 2002 [25] | + | - | + | - | - | - | - | - | - | - | + | + | - | + | + | 52 | + | - | 50 | + | + | + | - | + | + | + | + | + | + | + | + | + | 96 | 66 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Kubo et al., 2003 [63] | + | + | + | + | - | - | - | - | - | - | + | / | / | + | + | 86 | + | - | 50 | + | + | + | - | + | + | + | + | + | + | + | + | + | 96 | 77 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Kubo et al., 2006a [40] | + | - | + | - | - | - | - | + | - | + | + | + | - | + | - | 49 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | - | 95 | 65 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Kubo et al., 2006b [87] | + | - | + | + | + | - | - | + | - | + | + | + | + | + | + | 80 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 77 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Kubo et al., 2006c [88] | + | - | + | - | + | - | - | + | - | + | - | + | + | + | - | 56 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | - | 95 | 67 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Kubo et al., 2007 [59] | + | - | + | - | - | - | - | + | - | + | + | + | - | + | + | 56 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 69 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Kubo et al., 2009 [60] | + | - | + | - | + | - | - | + | - | + | - | + | + | + | - | 56 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | - | 95 | 67 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |
Kubo et al., 2010 [52] | + | - | + | + | - | - | - | + | - | + | + | + | + | + | + | 78 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 76 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Kubo et al., 2012 [72] | + | - | + | + | - | - | - | + | - | + | + | + | + | + | - | 70 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 73 | Unclear | Unclear | Unclear | Yes | Yes | Yes |
Malliaras et al., 2013 [41] | + | + | + | + | + | - | - | + | - | + | + | - | - | + | + | 80 | + | - | 50 | + | + | + | + | + | + | + | + | + | + | + | + | + | 100 | 77 | Unclear | Yes | Yes | Yes | Yes | Yes |
Seynnes et al., 2009 [30] | + | + | + | - | + | - | - | + | + | - | - | + | + | + | + | 78 | + | - | 50 | + | + | + | - | + | + | + | + | + | + | + | + | + | 96 | 74 | Unclear’ | Unclear’ | Unclear | Yes | Yes | Yes |