Association between Hamstring Flexibility and Sprint Speed after 8 Weeks of Yoga in Male Rugby Players

Abstract

Background:
A Yoga-asana-based intervention has demonstrated its ability to improve flexibility of individuals, but has not been explored in rugby players. We hypothesized that a structured yoga intervention may have an effect on flexibility and sprint performance in male rugby union players.

Methods:
It was a controlled trial research design and players were assigned using random sampling to one of the two groups; a yoga group (n = 16) that practised yoga for 1 h 2 times a week for 8 weeks in addition to their normal rugby training and a control group (n = 15) with regular rugby training but no yoga intervention. Yoga intervention included 32 yoga postures to address both the upper and lower extremities of the body. Data were collected during preseason and mid-season on hamstring flexibility (sit and reach test), and sprint performance (measured at 5, 10, and 30 m).

Results:
One hundred and twenty participants were screened and thirty-one players volunteered for the study. Interactions between groups and differences between pre- and post-intervention scores were analyzed using analysis of variance using SPSS (version 24.0). Significance was set at an alpha level of P = 0.05. The yoga group showed a small nonsignificant decrease (-1.2% ± 21.4%, P = 0.05) in hamstring flexibility compared to the control group which demonstrated a large significant decrease (-14.8% ± 23.7%) (mean % change ± 95% confidence interval [CI], P < 0.05). The yoga group also showed minor nonsignificant improvements in sprint times -3.2% ± 10.4%, -0.7% ± 9.0% for the 5 and 10 m sprints, respectively, (mean % change ± 95% CI) compared to controls -0.4% ± 10.2%, 0.4% ± 7.9%.

Conclusions:
Findings suggest that completing a structured yoga intervention alongside normal rugby training during the rugby season, yoga helped rugby players maintain their hamstring flexibility but did little to improve sprint performance during the season.

Full text

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
© 2021 International Journal of Yoga | Published by Wolters Kluwer ‑ Medknow72
Introduction
Flexibility is a vital factor that has been
associated with improved performance[1]
and reduced sports‑related injuries.[2] Many
coaches, physicians, and trainers have
accepted the important role exibility plays
in sports and have included exercises to
increase and maintain exibility in warm‑up
sessions before sports activity.[1] However,
researchers have reported mixed results
when examining the eects of exibility
on speed, athletic performance, and
countermovement jump performance.[1,3‑6]
These mixed results have created confusion
and debate among researchers, particularly
around the association stretching has with
subsequent explosive performance.[4,7‑9] To
date, only a few researchers have explored
the chronic eect of a stretching routine or
exibility intervention on rugby players.[10]
Address for correspondence:
Mr. Tilak Raj,
P.O. Box: 85084, Lincoln 7647,
Canterbury, New Zealand.
E‑mail: tilakraj.tilakraj@
lincolnuni.ac.nz
Access this article online
Website: www.ijoy.org.in
DOI: 10.4103/ijoy.IJOY_79_20
Quick Response Code:
Abstract
Background: A Yoga‑asana‑based intervention has demonstrated its ability to improve exibility of
individuals, but has not been explored in rugby players. We hypothesized that a structured yoga
intervention may have an eect on exibility and sprint performance in male rugby union players.
Methods: It was a controlled trial research design and players were assigned using random sampling
to one of the two groups; a yoga group (n = 16) that practised yoga for 1 h 2 times a week for
8 weeks in addition to their normal rugby training and a control group (n = 15) with regular rugby
training but no yoga intervention. Yoga intervention included 32 yoga postures to address both the
upper and lower extremities of the body. Data were collected during preseason and mid‑season on
hamstring exibility (sit and reach test), and sprint performance (measured at 5, 10, and 30 m).
Results: One hundred and twenty participants were screened and thirty‑one players volunteered for
the study. Interactions between groups and dierences between pre‑ and post‑intervention scores were
analyzed using analysis of variance using SPSS (version 24.0). Signicance was set at an alpha level
of P ≤ 0.05. The yoga group showed a small nonsignicant decrease (−1.2% ± 21.4%, P = 0.05)
in hamstring exibility compared to the control group which demonstrated a large signicant
decrease (−14.8% ± 23.7%) (mean % change ± 95% condence interval [CI], P < 0.05). The
yoga group also showed minor nonsignicant improvements in sprint times −3.2% ± 10.4%,
−0.7% ± 9.0% for the 5 and 10 m sprints, respectively, (mean % change ± 95% CI) compared to
controls −0.4% ± 10.2%, 0.4% ± 7.9%. Conclusions: Findings suggest that completing a structured
yoga intervention alongside normal rugby training during the rugby season, yoga helped rugby
players maintain their hamstring exibility but did little to improve sprint performance during the
season.
Keywords: Acceleration, performance, range of motion, stretching
Association between Hamstring Flexibility and Sprint Speed after 8 Weeks
of Yoga in Male Rugby Players
Short Communication
Tilak Raj,
Michael J Hamlin1,
Catherine A Elliot1
Department of Tourism, Sport
& Society, Lincoln University,
1 Department of Tourism,
Sport & Society, Faculty of
Environment, Society and
Design, Lincoln University,
Lincoln, New Zealand
How to cite this article: Raj T, Hamlin MJ, Elliot CA.
Association between hamstring exibility and sprint
speed after 8 weeks of Yoga in male rugby players.
Int J Yoga 2021;14:XX-XX.
Submitted: 12-Jul-2020 Revised: 09-Sep-2020
Accepted: 22-Dec-2020 Published: ***
Yoga is a combination of physical postures
(Asana), breathing exercises (Pranayama),
and meditation (Dhyana), which focuses
on the physical and mental aspects of
an individuals’ movements.[11] Improved
exibility is one of the major benets of
yoga practice and yoga has been shown
to have similar eects compared to
stretching exercises.[12] This study employed
Hatha‑yoga, which uses various body
positions to stretch muscles in conjunction
with an emphasis on controlled breathing
exercises.
The aim of the study was, therefore,
to assess whether a yoga (stretching)
intervention practised by male rugby
players alongside their usual rugby training
had any eect on their subsequent exibility
and sprint performance.
IJOY_79_20R6_OA
This is an open access journal, and arcles are
distributed under the terms of the Creave Commons
Aribuon‑NonCommercial‑ShareAlike 4.0 License, which
allows others to remix, tweak, and build upon the work
non‑commercially, as long as appropriate credit is given and
the new creaons are licensed under the idencal terms.
For reprints contact: WKHLRPMedknow_reprints@wolterskluwer.com

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
Raj, et al.: Yoga and rugby performance
73International Journal of Yoga | Volume 14 | Issue 1 | January-April 2021
Methods
Participants
Initially, 120 players were screened, and 31 male rugby
players (19.5 ± 0.9 years) [Table 1] from a local rugby
union football club volunteered for the study [Figure 1].
However, only nineteen players (yoga n = 12) (control
n = 7) completed the study due to injuries and personal
circumstances. All players were novices to the practice
of yoga. Players were randomly assigned either to the
yoga group (practised yoga for 1 h, two times/week for
8 weeks in addition to their normal rugby training) or the
control group (continued with their normal rugby training
without yoga). All players were free from any current or
previous injuries. All players were also informed about the
possible risks of volunteering for this study and provided
written informed consent before the study. Following the
Declaration of Helsinki, this research was approved by the
Institutional Human Ethics Committee.
Design of the study
A yoga intervention was exclusively designed for rugby
players and delivered by a yoga instructor (registered
exercise professional, New Zealand). Players were required
to complete 3, 30 m sprints to measure the physical
performance. All participants were in the same yoga class,
and all sessions were completed in a large open tness
room.
Assessment
Flexibility of the hamstrings
A baseline examination was carried out 1–2 weeks before
the yoga intervention and again 1–2 weeks after the last
yoga session. The hamstring exibility of players was
measured in a seated position in front of a Flex‑Tester©
box (Novel Products, Inc.; Rockton, IL, USA). The
hamstring exibility test consisted of 3 sit‑and‑reach tests.
Players were not allowed to ex their knees during the test
and players were required to have a 2 min rest between
each attempt with the best attempt used in the analysis.
Sprint performance
After completing the hamstring exibility test, sprint
performance was measured using three 30‑m sprints. The
Table 1: Physical characteristics and playing experience
of the yoga and control groups
Group Yoga group Control group
Age (years) 19.1±0.9 19.6±0.9
Height (cm) 181.3±8.1 182.7±4.1
Weight (kg) 88.9±18.7 85.5±9.4
BMI (/m2)26.6±5 26.6±3.3
Rugby experience (years) 4.0±1.3 3.5±1.3
Data are mean±SD. SD: Standard deviation
Allocation
Analysis
Enrolment
Assessed for eligibility (n = 120)
Excluded (n = 89)
• Not meeting inclusion criteria (n = 40)
• Declined to participate (n = 30)
• Prior yoga experience (n = 10)
• Other reasons (n = 9)
Randomised (n = 31)
Allocated to Yoga Group (n = 16)
Received allocated intervention alongside
their regular rugby training and asked
not to do any additional physical activity
Allocated to Control Group (n = 15)
Asked not to perform any physical activity
other than the regular rugby training
Follow-up
Lost to follow-up (personal reasons) (n = 1)
Discontinued intervention due to injury (n = 3)
Lost to follow-up (personal reasons) n = 3)
Discontinued intervention due to injury (n = 5)
Analysed (n = 12) Analysed (n = 7)
Figure 1: Flowchart describing the selection and categorisation of subjects from the rugby clubs for the present analysis

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
Raj, et al.: Yoga and rugby performance
74 International Journal of Yoga | Volume 14 | Issue 1 | January-April 2021
sprint was analyzed in two acceleration phases (5 and 10 m)
and maximal velocity (30 m).[13] Each participant completed
the sprint from a standing start position. Sprint time (to
the nearest 0.01 s) was recorded using a set of electronic
speed‑timing lights placed at 5, 10, and 30 m (SmartSpeed,
Fusion Sport Ltd., Australia). A 2 min recovery was
required between each sprint, and the best of 3 attempts
was used in the analysis. All players were asked not to
perform any strenuous exercise in the 24 h before testing.
The testing was completed at the same time of day on a
large covered slip‑free oor area under similar climatic
conditions.
Intervention
Yoga classes were oered two times a week for 8 weeks,
which started at the beginning of the rugby season.
The average attendance rate for the yoga group was
75% (12 sessions), with some players attending all (16)
sessions, whereas others only attended (9) sessions. Each
yoga session consisted of a warm‑up of 10 min with
Surya‑namaskar (dynamic stretching sequence of postures)
followed by 35 min of yoga postures (10 min standing,
10 min sitting, and 15 min of supine and prone postures
and a mix of static and dynamic postures) and 10 min
relaxation in the nal resting position (lying in the supine
position without any stretching exercise). A total of 5 min
was allocated for the transition between the yoga postures.
Data extraction
The mean of the fastest sprint time and highest exibility
scores of individual players at pre‑ and post‑testing were
recorded on Excel and later were used in the group
analyses.
Data analysis
The number of participants required for the study was
calculated using a spreadsheet with the smallest worthwhile
change in performance being 1.0% and the typical error
or within‑subject standard deviation (SD) in similar
tests of 0.7%. This calculation estimated we needed 7
participants in each group in a controlled trial research
design. Interactions between group and dierences between
pre‑ and post‑intervention scores were analyzed using
analysis of variance. Statistical analyses were performed
using SPSS 24 for Windows (SPSS, Inc., Chicago, IL,
USA). Signicance was set at an alpha level of P ≤ 0.05.
Data given represents the mean ± SD unless stated
otherwise.
Results
The yoga group showed a small decrease
(−1.2% ± 21.4%) in hamstring exibility compared to the
control group which demonstrated a signicant decrease
(−14.8% ± 23.7%) (mean % change ± 95% condence
interval [CI], P < 0.05). In addition, the yoga group showed
a small, but nonsignicant improvement of 3.2% ± 10.4,
and −0.7% ± 9.0%, in their sprint time when compared to
the control group –0.4% ± 10.2%, 0.0% ± 7.9%, in 5 and
10 m, respectively [Table 2].
Discussion
This study found that rugby players that undertook 8 weeks
of static and dynamic stretching during a weekly 1‑h yoga
intervention, in addition to their normal rugby training
sessions, either maintained or had a minimal decrease in
their hamstring exibility compared to players who did
the rugby training only. However, this exibility training
through the yoga intervention did little to improve short
sprint performance between the groups (e.g., 5, 10, and
30‑m sprint time), we found no signicant benecial
improvement in sprint performance in the experimental
group (receiving yoga intervention) compared to controls.
The controversial issue of stretching to improve
performance is based on several postulated mechanisms.
Dynamic movement requires the contraction and elongation
of the muscle‑tendon unit (and thereby, movement
of the limb around the joint). This shortening and
stretching (stretch‑shortening cycle), relies on the elastic
proprieties of the tendon to enable the release of potential
energy. Hence, the elastic property of the muscle‑tendon unit
is crucial and is inuenced by the stiness of both tissues.
It is believed that greater compliance (i.e., less stiness) in
these tissues improves energy storage, thereby enhancing
muscle performance.[14] Given that the stretching (yoga)
group improved exibility, compared to the control group,
which may have increased muscle compliance, this did not
seem to change muscle performance during sprinting in the
rugby players measured in this study. This suggests that
either tissue compliance did not change (and the relative
Table2:Hamstringexibilityand5,10,30msprinttimeoftheyogaandcontrolgroup
Control group Yoga group Between group pre
post (%) change
(±95%CI)
Pre (n=7) Post
(n=7)
Control group pre post
(%)change(±95%CI)
Pre
(n=12)
Post
(n=12)
Yoga group pre post
(%)change(±95%CI)
Flexibility (cm) 32.3±9.4 26.0±12.9 −14.8 (23.7) 31.1±11.1 30.9±9.4 −1.2 (21.4) 17.3 (30.8)*
5 m Sprint (s) 1.01±0.07 1.01±0.15 −0.42 (10.21) 1.07±0.05 1.04±0.14 −3.2 (10.4) −2.7 (10.4)
10 m Sprint (s) 1.78±0.11 1.80±0.23 0.37 (7.85) 1.82±0.14 1.81±0.20 −0.7 (9.0) −1.1 (8.4)
30 m Sprint (s) 4.35±0.27 4.57±0.60 4.37 (7.13) 4.52±0.31 4.54±0.40 0.2 (5.4) −4.1 (6.7)
Data are raw mean±SD of each group with the dierence within and between groups given as the percent mean dierence±95% CI.
*Statically signicantly (P<0.05). SD: Standard deviation, CI; Condence interval

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
Raj, et al.: Yoga and rugby performance
75International Journal of Yoga | Volume 14 | Issue 1 | January-April 2021
increase in exibility is due to other mechanisms), or
that there is little eect of increased compliance on sprint
performance. On the other hand, while the yoga group
showed an increase in exibility compared to the control
group (an average of 17.3%), in reality, the signicant
change between groups is probably because the exibility in
the control group decreased (−14.8%) while the exibility
in the yoga group changed little (−1.2%). Therefore, if the
exibility did not change in the yoga group, we would not
expect to nd greater muscular compliance and thus little
change in performance.
Previous research has found that yoga practiced for 75 min
two times/week for 20 weeks (average of 150 min/week)
improved sit and reach scores by approximately 13 cm
in the rst 10 weeks and 17 cm at the end of training
in healthy adults.[15] The players in the current study
completed approximately 90 min/week for 8 weeks
which may indicate a larger stretching dose is required
to achieve signicant exibility changes. In addition, not
all players in the current study made every yoga session
with an attendance rate of only 60% compared to 78%
in the Petric’s[15] study. Overall, this would suggest the
players in the current study received substantially less
muscle stretching time which resulted in a lower stretching
dose and therefore less muscle adaptation. We would
recommend that any future studies in this area should allow
players to complete at least 150 min of yoga per week.
Whether the 150 min per week of muscle stretching (for a
minimum of 12 and up to 20 weeks) can successfully be
incorporated into shorter sessions (e.g. 30 min on 5 days/
week) requires further investigation.
It is also possible, that due to muscle damage suered
either at training or during a match, which can result in
substantial swelling and edema,[16] the eectiveness of any
chronic stretching intervention, was reduced. We speculate
that perhaps the stretching employed in the current study
by the yoga group was enough to buer any losses in sprint
performance associated with such muscle damage since the
yoga group sprint times did not decrease as much as the
control group sprint times. However, this is speculative and
would require further research before this theory can be
conrmed.
Conclusions
Yoga practiced for 1 h twice a week over an 8‑week period
was sucient enough to maintain hamstring exibility
in male rugby players compared to players that did not
complete yoga; however, the maintenance of exibility
did not result in any signicant improvement in sprint
performance in these players. We would recommend
that any stretching intervention (including yoga) should
be practiced for at least 150 min/week over a longer
period (i.e., 20 weeks) to allow adaptations to occur which
may result in muscular performance change.
Acknowledgment
We would like to thank the coaches and participants of the
study for their time.
Financial support and sponsorship
Nil.
Conictsof interest
There are no conicts of interest.
References
1. Fletcher IM, Anness R. The acute eects of combined static and
dynamic stretch protocols on fty‑meter sprint performance in
track‑and‑eld athletes. J Strength Cond Res 2007;21:784‑7.
2. Shellock FG, Prentice WE. Warming‑up and stretching for
improved physical performance and prevention of sports‑related
injuries. Sports Med 1985;2:267‑78.
3. Yuktasir B, Kaya F. Investigation into the long‑term eects of
static and PNF stretching exercises on range of motion and jump
performance. J Bodyw Mov Ther 2009;13:11‑21.
4. Paradisis GP, Pappas PT, Theodorou AS, Zacharogiannis EG,
Skordilis EK, Smirniotou AS. Eects of static and dynamic
stretching on sprint and jump performance in boys and girls.
J Strength Cond Res 2014;28:154‑60.
5. Sayers AL, Farley RS, Fuller DK, Jubenville CB, Caputo JL.
The eect of static stretching on phases of sprint performance in
elite soccer players. J Strength Cond Res 2008;22:1416‑21.
6. Skaggs JR, Joiner E, Pace J, Sini M, Skaggs D. Is exibility
associated with improved athletic performance? J Sci Med
Central 2015;21:1010.
7. Shrier I. Does stretching improve performance? A systematic and
critical review of the literature. Clin J Sport Med 2004;14:267‑73.
8. Gleim GW, McHugh MP. Flexibility and its eects on sports
injury and performance. Sports Med 1997;24:289‑99.
9. Fletcher IM, Jones B. The eect of dierent warm‑up stretch
protocols on 20 meter sprint performance in trained rugby union
players. J Strength Cond Res 2004;18:885‑8.
10. Darrall‑Jones JD, Jones B, Till K. Anthropometric and physical
proles of english academy rugby union players. J Strength
Cond Res 2015;29:2086‑96.
11. Brunelle JF, Blais‑Coutu S, Gouadec K, Bédard É, Fait P.
Inuences of a yoga intervention on the postural skills of the
Italian short track speed skating team. Open Access J Sports
Med 2015;6:23‑35.
12. Gothe NP, McAuley E. Yoga is as good as stretching‑strengthening
exercises in improving functional tness outcomes: Results from
a randomized controlled trial. J Gerontol A Biol Sci Med Sci
2016;71:406‑11.
13. Darrall‑Jones JD, Jones B, Till K. Anthropometric and physical
proles of english academy rugby union players. J Strength
Cond Res 2015;29:2086‑96.
14. Wilson GJ, Elliott BC, Wood GA. Stretch shorten cycle
performance enhancement through exibility training. Med Sci
Sports Exerc 1992;24:116‑23.
15. Petric M, Vauhnik R, Jakovljevic M. The impact of hatha
yoga practice on exibility: A pilot study. Altern Integr Med
2014;3160:2‑10.
16. Järvinen TA, Järvinen M, Kalimo H. Regeneration of injured
skeletal muscle after the injury. Muscles Ligaments Tendons J
2013;3:337‑45.