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R E S E A R C H A R T I C L E Open Access
Effects of nine weeks isokinetic training on
power, golf kinematics, and driver
performance in pre-elite golfers
James Parker
1,2*
, Charlie Lagerhem
1
, John Hellström
1,3
and M. Charlotte Olsson
1
Abstract
Background: It has previously been shown that isotonic strength training can improve driver performance among
golfers, though few studies have investigated effects of strength training on swing kinematics together with driver
performance. In this study we investigated whether isokinetic rotational training could improve driver performance
and swing kinematic variables amongst elite golfers.
Methods: Twenty competitive pre-elite golfers (handicap better than −3.0), 13 men and 7 women, were split into
two groups, one group received the isokinetic power training (IK) alongside their normal isotonic pre-season
strength-training and the other group continued with their normal isotonic pre-season strength-training regime (IT).
The IK group completed 12 sessions of isokinetic power training on a standing rotation exercise (10% body weight at
1 m/s) and barbell squat (25 kg plus 10% body weight at 0.5 m/s). The IT group continued with their normal isotonic
pre-season strength-training regime. Participants were tested for rotational power, lower body power, golf
swing kinematics, and driver performance before and after a nine-week training period.
Results: After the nine-week training period both the IK and the IT groups increased their dominant side rotational
force and power (effect sizes between 0.50–0.96) and magnitude based inference indicated that IK had a likely (> 80%)
more beneficial increase in dominant side rotational force and power. For swing kinematics, IK had a likely (> 80%)
more beneficial improvement in lead arm speed and acceleration compared to the IT group. For driver performance, IK
had a possible (65%) beneficial effect on ball speed and likely (78%) beneficial effect on carry distance when compared
to IT, whereas neither of the groups improved club head speed.
Conclusion: In the present study on pre-elite golfers we found that 9 weeks of isokinetic training increased seated
rotational force and power, peak arm speed and arm acceleration, ball speed, and carry distance more compared to
isotonic training. Even though isokinetic training did not increase CHS, it did result in greater carry distance.
Keywords: Golf biomechanics, Isokinetic training, Power, Driver performance, Kinematics, Performance gains
Background
In competitive golf, the player’s ability to hit the ball a
long distance affects the score in a positive way [1], and
research highlights the importance of driving distance in
relation to golf performance [2]. Initial ball velocity is
dependent on centeredness of impact, club head velocity
(i.e. magnitude and direction) and club face orientation
[3–5]. Most research investigating driving performance
in golf report a strong correlation between club head
speed (CHS), initial ball velocity and thus carry (striking
distance from impact to landing, excluding roll) [6, 7].
Recent research [8] reports kinematics, segmental
sequence of action, and power output as other important
factors impacting on driving performance. Thus, many
golfers incorporate strength and power training into
their training schedule in order to positively influence
their swing kinematics. However, there is a paucity of re-
search into these training strategies and a better under-
standing of how muscular strength and power training
* Correspondence: james.parker@hh.se
1
The Rydberg Laboratory for Applied Sciences, School of Business,
Engineering and Science, Halmstad University, Box 823, 301 18 Halmstad,
Sweden
2
Scandinavian College of Sport, Box 11365, 494 28 Gothenburg, Sweden
Full list of author information is available at the end of the article
© The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0
International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and
reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to
the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver
(http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21
DOI 10.1186/s13102-017-0086-9
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
influence golf swing kinematics and driving performance
in elite golfers is required.
Many studies have investigated the correlation between
physical capacities and different measures of driver per-
formance including CHS, ball speed, and driving distance
[9–15]. These correlational studies only measure associa-
tions between variables and give little information about
which variables can be improved through training. Longitu-
dinal studies following changes in both physiological
characteristics and driver performance in golf are better
able to describe likely cause and effect relationships. Previ-
ous strength training interventions in different golf popula-
tions have included general strength exercises performing
twotothreesetsof10–12 repetitions performed two to
three times a week over eight to 10 weeks and these studies
found improvements in CHS and driving distance among
recreational golfer [16–20], and in CHS amongst elite
golfers [21]. There is a scarcity of research using fewer exer-
cises and specific rotational exercises, rather than a multi-
tude of general strength training exercises, despite the
rotational nature of the golf swing. Only a few studies have
included rotational tests or incorporated training exercises
aimed to mimic the ballistic movements in the golf swing
and they found marginal changes in CHS (1.5–1.6%) and in
driving distance (4.3%) [16, 21]. Intervention studies using
strength training in golf have received some criticism for a
lack of research on skilled golfers and inclusion of control
groups [1, 8]. The most common performance variable
measured is CHS, however a review [8] found that ball
speed was the driver performance variable most likely to
increase from a strength training intervention. Outcome
measures are mostly driver performance variables and do
not include swing kinematic variable. Including measure-
ment for swing kinematics would allow for a better under-
standing of the causality of improvement in driver
performance from strength training.
Most strength and power intervention studies in golf
have used driver performance variables as their outcome
measurements whereas swing kinematic variables are
rare [17]. The ability to generate and coordinate force
through hips, torso, and shoulders during the down-
swing influences both swing kinematics and driver per-
formance. It is therefore useful to understand how
training influences not only driver performance but also
the swing kinematics. Previous strength training [17],
and motor control [22, 23] intervention studies which
have investigated both changes in swing kinematics and
driver performance have studied mainly male recre-
ational level golfers (one female participant in total [23]).
These studies found a significant reduction (−13%) in
pelvis torso axial rotation at top of backswing (x-factor)
[17]; a 2.7°- increase in pelvis-thorax separation during
the early downswing (x-factor stretch) [22]; a 14%
increase in pelvis, torso, and wrist velocity [17, 22]; and
an increase in driver performance variables including
CHS [17], ball speed [17], and carry distance [17, 22].
These studies indicate that for amateur golfers, reducing
x-factor and increasing x-factor stretch have a positive
impact on driver performance, however, if this holds true
for high-level golfers as well is not known. Bulbulian et
al. [23] included one woman out of seven participants
and no other training intervention investigating swing
kinematics has included women golfers. Cross-sectional
studies comparing men and women golfers have found a
number of differences in both physiological and golf
swing kinematic variables. Horan et al. [24] studied
movement variability and found that women exhibited
higher variability in thorax-pelvis coupling mechanics
during the downswing variability when compared to
men but both groups showed similar end-point trajec-
tory variability (hands and clubhead). Egret et al. [25]
assessed differences in swing kinematics between experi-
enced (average handicap −6.3) male and female golfers
and found specifically hip and shoulder joint rotation
angles at top of backswing differed between groups.
Interestingly, they did not find any difference in club-
head speed. Zheng et al. [26], compared swing kinemat-
ics between male and female golfers on the PGA and
LPGA tour and found differences in particular in max-
imum velocity of the wrists, right elbow extension, tim-
ing of left wrist extension velocity, and club head
velocity. A greater X-factor stretch is assumed to make
use of the stretch-shortening cycle (SSC), where a
greater stretch of the torso musculature is assumed to
allow for greater forces to be developed [1, 22]. Bulbu-
lian et al. [23] reported a reduced electromyography ac-
tivity in the torso and no change in driver performance
after an intervention to shorten the backswing. These
authors proposed that performance may have been
maintained by increased loading of the shoulder muscu-
lature instead of torso musculature. Aside from the
shoulder, performance maintenance may have been
maintained by an increase in work done both below
(lower body musculature) and/or above (upper body,
shoulders, and arms) the torso. There is a paucity of re-
search in physical training interventions on high-level
golfers, which also study how the training intervention
influence swing kinematics including the shoulder in
addition to the pelvis-thorax segments.
Until recently, most strength and power intervention
studies investigating isokinetic training in general, have
used single joint movements [27] with only a few studies
investigating multi-joint isokinetic training [28, 29]. In
comparison to traditional isotonic training, isokinetic
training, which is often performed at very low speeds
(0.1–0.4 m/s), has the advantage that near maximal force
can be exerted throughout the entire range of motion
[28]. Similar to results from single joint isokinetic training,
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 2 of 12
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studies using multi-joint isokinetic training showed
improved peak force and performance in dynamic move-
ments [28, 29]. A recent study compared isotonic and
isokinetic multi-joint (squat) training in different team
sports athletes [28] and found that isokinetic multi-joint
training improved select performance variables such as
sprint and drop jump to a greater extent than traditional
isotonic training. The use of multi-joint isokinetic training
in a golf-specific movement and its influence on swing
kinematics and driver performance among high-level
golfers has not been studied previously. Thus, the purpose
of this study was to investigate if isokinetic rotational and
lower body strength training over 9 weeks is more effective
than isotonic strength training in improving rotational and
lower body power, pelvis-thorax and shoulder kinematics,
and driver performance among high-level golfers.
Methods
Participants
Twenty intercollegiate golfers (13 men and 7 women) all
competing at a national level or higher participated in
the study. All subjects reported a handicap of −3.0 or
better registered with the Swedish golf association at the
time of the study. All subjects were free of musculoskeletal
injuries for the previous 12 months and had a minimum of
3 years golf-specific strength training experience. The sub-
jects did not all have the same swing coach. The study
design was an open trial study since the participants
could choose which group to belong to. Their choices
were mainly based on individual travelling schedules
and distance to the training facility during the
investigation period.
There were no drop-outs in the study. This study was
approved by the regional Swedish ethics committee (Lund,
Dnr 2016/12) and all the participants gave written consent
to participate in the study.
Procedures
A training study was designed to investigate the differ-
ence between isotonic and isokinetic power training in
golf. The load for the isokinetic group was controlled by
a computerized robotic engine system (1080 Quantum
Synchro, 1080 Motion AB, Lidingö, Sweden). The
advantage of computerized robotic engine system is that
isokinetic resistance can be applied to functional multi-
joint exercises, such as golf specific rotational exercise
and loaded squats [28].
Training
The participants were divided into two groups, one group
(n= 10, 6 men and 4 women) received the isokinetic
(constant-speed) power training (IK) and the other group
(n= 10, 7 men and 3 women) continued with their normal
isotonic (constant load) pre-season strength-training regime
and served as the reference isotonic group (IT).
The training period lasted 9 weeks, with 1 week of
cessation in the middle of the period to accommodate
competition calendars. Both groups resistance trained
on average three times a week and had individualised
programs of isotonic and isometric exercises performed
both with free weights and body weight resistance as
well as ballistic rotation exercises performed during the
nine-week period. For the IK group, two isokinetic exer-
cises replaced the ballistic rotation exercises and isotonic
power exercises in their regular training program, where
isokinetic power training was performed on average
twice a week. The two isokinetic exercises, performed in
a computerised robotic engine system, consisted of an
isokinetic standing rotation exercise designed to repli-
cate the golf swing and a loaded isokinetic squat. Both
isokinetic exercises consisted of three sets of five repeti-
tions where the isokinetic rotation exercise was per-
formed with 10% body weight resistance and the speed
set at 1 m/s concentrically and 4 m/s eccentrically. The
loaded squat was performed with 25 kg barbell plus 10%
body weight resistance and the speed set at 0.5 m/s
concentrically and 4 m/s eccentrically.
Tests
All tests were performed just before the beginning of the 9
week training intervention and within 1 week of the last
training session.
Power testing Lower and upper body power tests were
assessed using countermovement jumps with arm swing
(CMJ), loaded squat jumps, and sitting abdominal rota-
tion. Participants performed three repetitions on each
test with 5 min rest between the repetitions; the repeti-
tion with the highest value on each weight was recorded.
The countermovement jumps were performed indoors,
measurements of jump height were recorded with the
use of infrared sensors (Ivar jump and speed analyzer,
LN sport consult, Sweden). The subjects were instructed
to stand in an upright position with their feet in a
shoulder-width stance. The jump was initiated with a
countermovement motion and continued in an explosive
upward motion with the assistance of the arms. During
the landing, the subjects aimed at finishing at the same
position as the jump was initiated from.
Loaded squats jumps were performed with 20, 40 and
60 kg load on the shoulders. The subjects performed squat
jumps from a 90° knee angle to full extension. Measure-
ments of peak power were collected with the use of a linear
encoder (MuscleLab, Model 4000, Ergotest Technology,
Norway). For data analysis, only the 20 kg loaded squat
jump was used since some participants were unable to
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conduct a technically correct and safe loaded squat jump
at the higher loads.
Measurements of sitting isotonic abdominal rotational
power were obtained in 1080 Quantum. The test used in
this study consisted of a modified version of the test by
Andre et al. [30]. The subjects were instructed to sit on
a bench (height 46 cm, length 100 cm) with their feet on
the floor. The bench was placed 125 cm from the handle
which was set at shoulder height. The subjects were
instructed to grip the handle and rotate their torso force-
fully, with straight arms, and then slowly return to the
starting position. Three repetitions on the left side and
three repetitions on the right side were performed using a
load of 10% of body weight. Rotating to the left was classi-
fied as the dominant side for a right-handed golfer as this
is the same direction as they perform in the golf swing,
and thus of main interest in this study. The highest peak
force, power, and velocity value of the three repetitions on
each side was used for later analyses.
Golf Swing analysis: All golf tests were performed at a
driving range where subjects hit out onto a driving range.
Swing kinematic data was using a four sensor electromag-
netic motion capture system at 240 Hz (Polhemus Inc.
Colchester, VT, USA) together with Advanced Motion
Measurement software (AMM 3D, Phoenix, Arizona,
USA) equipment previously used in golf research [31, 32].
The orientation of the right-handed orthogonal global co-
ordinate system was such that the positive x-axis pointed
parallel to the shot direction, the positive z-axis vertically
upwards, and the positive y-axis forward from the right-
handed golfer. The kinematics variables are described in
Table 1 and placement of the sensors and digitization are
described in Table 2. Thorax and pelvis rotations were
calculated using the joint coordinate system method
[33]. The lead arm segment was calculated using the
humerus joint coordinate system (first option) [34]
relative to the thorax.
The subjects used their own golf club and premium
Callaway range balls and were told to aim at a target set
approximately 350 m away from the striking zone. All
subjects performed a golf specific warm up of their
choice for a maximum of 10 min. Subjects were then
instructed to hit 5 balls with their driver and use the
swing that was as ‘normal ‘as possible, for example when
playing from a tee on a standard par-4 hole. Between
each shot, subjects were instructed to walk out of the
tee (strike) area and wait for 30 seconds before com-
mencing their pre-shot routine for the subsequent trial.
We chose to use a five trial procedure primarily due to
the participants’time constraints, and such five trial pro-
cedures have been used in previous research [24, 35].
The swing where highest CHS was achieved was then
used for subsequent analysis. Golf ball launch analysis:
CHS, ball speed, and carry distance data were collected
using a launch monitor (Trackman3e, v.3.2, Trackman,
Denmark) placed 2.5 m behind the golf ball.
Statistical analysis
All results are reported as mean ± standard deviation
(SD). A probability level of 0.05 was used in this study.
Table 1 A description of how swing kinematic variables were
determined
Definitions
Transition Is determined as the point of lowest angular velocity
for a segment, between initiation of the backswing
and impact.
X-factor The change in amplitude of spinal rotation
(difference between thorax and pelvis rotation) at
pelvis transition
X-factor
stretch
The maximum increase in X-factor during the
downswing
X-factor
stretch rate
The average speed of X-factor stretch
Shoulder
stretch
The change in amplitude of lead arm horizontal
adduction between thorax transition and lead arm
transition
Shoulder
stretch rate
The average speed of shoulder stretch
Pelvis
acceleration
The average acceleration of the pelvis between pelvis
transition and pelvis peak speed
Thorax
acceleration
The average acceleration of the thorax between
thorax transition and peak thorax speed
Lead arm
acceleration
The average acceleration of the lead arm between
lead arm transition and lead arm peak speed, measured
around the local Z-axis at the shoulder joint
Table 2 Placement of magnetic sensors and description of
landmarks used to create each segment
Segment Sensor
placement
Landmarks used for segment
digitization
Club Below Ggrip Top of grip.
Hozel.
Club head, bottom groove at heel.
Club head, bottom grove at toe.
Club head, top groove at toe.
Left arm Posterior upper
arm
Left acromion process.
Lateral epicondyle
Medial epicondyle.
Thorax/Upper-
body
On T5 Left acromion process.
Right acromion process.
Right side mid thorax, high.
Right side mid thorax, low.
Pelvis Sacrum Left greater trochanter.
Right greater trochanter.
The point above left greater
trochanter.
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 4 of 12
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An independent t-test was performed to check for pre-
test differences between IT and IK groups and between
men and women. Since we could only recruit 7 female
participants to this study, statistical analyses divided by
sex, in the groups (IK = 4 and IT = 3 women) were not
feasible. However, in the result figures below we show
the individual values for each participant along with the
group mean to visualise change for the men and women
in the study. Magnitude based inference (MBI) was cal-
culated using an online published spreadsheet [36], in-
ferences were based on the disposition of the confidence
limit for the mean difference to the smallest worthwhile
change (0.2 between-subject SD). The probability that a
change in testing score was beneficial, harmful or trivial
was identified according to the magnitude-based infer-
ences approach [37]. Descriptors were assigned using
the following scales: 0–4.9% very unlikely; 5–24.9%
unlikely; 25–74.9% possibly; 75–94.9% likely; 95–
99.49% very likely; >99.5% most likely [38]. Within
group standardized mean difference effect size (ES
w
)
was calculated by using the mean change of the
group (ΔIT or ΔIK) in the numerator of the equa-
tion and using the pre-test pooled standard deviation
in the denominator. Pre-test pooled standard devi-
ation was calculated using pre-test values from the
sample as whole (both IK and IT) [39]. Between-
group standardized mean difference effect size (ES
b
)
was calculated by using the difference between IK
ES
w
and IT ES
w
. An effect size of 0.20–0.50 are con-
sidered “small”in magnitude, those > 0.50–0.80 are
“medium”and those above 0.80 are “large”as sug-
gested by Cohen [40]. AswellaspresentingESandre-
sults from MBI analysis this study presents standard
deviations and figures describing change for each partici-
pant (Fig. 1a–d) to improve the transparency of the
results.
Results
Based on previous studies [24–26] showing cross-
sectional differences in swing kinematics between men
and women, we analysed the pre-training measurements
variable for differences between sexes (Table 3). No dif-
ferences were found before the training period began
between men (n= 13) and women (n= 7) in swing
kinematic-related variables (p> 0.05), whereas both
-200
-100
0
100
200
300
400
500
600
Power (W)
IT IK
-30
-20
-10
0
10
20
30
40
50
Shoulder stretch rate ( /s)
IT IK
-100
-50
0
50
100
150
Lead arm speed ( /s)
IT IK
-4
-2
0
2
4
6
8
10
Ball speed m/s
IT IK
ab
cd
Fig. 1 a-d Change after the nine-week training period in (a) seated rotational power, (b) shoulder stretch rate, (c) lead arm peak speed, and (d)
ball speed after the nine-week training period for the isokinetic (IK) and isotonic (IT) groups. (Horizontal bars denote group means, circles signify
women, triangles signify men)
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 5 of 12
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power tests and performance measures differed between
sexes (Table 3) as would be expected in highly skilled
golfers [15, 21, 24, 26].
Differences before the training intervention between
the two training groups IK and IT were also investi-
gated and Table 4 shows that mean age, height,
weight and handicap between the two groups were
not different at the start of the study. In addition,
there was no statistically significant difference be-
tween groups before the training study began (p>
0.1) for any of the intervention related variables
assessed, including rotational and lower body power,
swing kinematics and driver performance variables
(Table 4).
Table 3 Descriptive statistics and an independent t-test on physical, kinematics, and driver performance variables for men and
women at the start of study
Men (n= 13) Women (n= 7) Sig p-value
Anthropometrics
Age (years)21.8 ± 2.1 22.8 ± 1.8 0.30
Height (cm) 178.7 ± 7.3 169.7 ± 5.6 0.01
Weight (kg) 76.8 ± 11.0 65.7 ± 9.6 0.04
Hhandicap +0.2 ± 1.5 +0.7 ± 1.0 0.40
Tests for power
CMJ (cm) 43.7 ± 7.1 35.0 ± 5.5 0.01
Seated rotation dominant side
Power (w) 793.8 ± 246.9 352.6 ± 96.8 0.00
Velocity (m/s) 3.5 ± 0.6 2.6 ± 0.3 0.00
Force (N) 261.8 ± 4.4 163.0 ± 27.2 0.00
Seated rotation non-dominant side
Power (w) 812.3 ± 231.7 366.9 ± 115.3 0.00
Force (N) 258.4 ± 36.6 169.3 ± 31.3 0.00
Velocity (m/s) 3.3 ± 0.6 2.6 ± 0.4 0.01
Kinematics
Pelvis speed (°/s) 458.3 ± 64.1 428.0 ± 51.3 0.30
Thorax speed (°/s) 712.5 ± 74.1 685.9 ± 62.8 0.43
Lead arm speed (°/s) 1050.5 ± 117.6 947.7 ± 87.3 0.06
Pelvis acceleration (°/s
2
) 2008.2 ± 556.9 1841.3 ± 316.2 0.48
Thorax acceleration (°/s
2
) 3310.9 ± 670.7 3392.7 ± 516.9 0.78
Lead arm acceleration (°/s
2
) 5433.5 ± 1196.7 5135.4 ± 947.2 0.58
X-factor (°) 49.2 ± 9.4 50.9 ± 10.4 0.71
X-factor stretch (°) 7.1 ± 5.5 11.7 ± 7.9 0.14
X-factor stretch rate (°/s) 44.0 ± 36.5 70.7 ± 38.4 0.14
Shoulder stretch (°) 1.7 ± 1.3 1.6 ± 1.5 0.85
Driver performance
Clubhead speed (m/s) 49.1 ± 3.1 41.6 ± 2.3 0.00
Ball speed (m/s) 68.5 ± 4.9 57.1 ± 3.6 0.00
Carry distance (m) 218.5 ± 22.7 179.9 ± 13.6 0.01
Values are mean ± standard deviation and p-values are from independent t-tests
Table 4 Descriptive statistics for the IK and IT group at the start
of study
IK Group (n= 10) IT Group (n= 10) p-value
Age (years) 22.0 ± 4.0 22.0 ± 4.0 0.45
Height (cm) 175.0 ± 13.0 178.0 ± 14.0 0.26
Weight (kg) 75.0 ± 22.0 71.0 ± 15.0 0.36
handicap +0.4 ± 1.0 +0.4 ± 1.7 0.90
Values are mean ± standard deviation and p-values are from independent t-tests.
IK isokinetic training group, IT isotonic training group
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Rotational and lower body power
In this study, both dominant and non-dominant side
force, velocity, and power were measured in the seated ab-
dominal rotation test. After the nine-week-training period,
both the IK and the IT groups increased their dominant
side rotational power to a large (ES
w
= 0.82) and medium
(ES
w
= 0.50) extent respectively (Fig. 1a, Table 5).
Between-group ES indicated a small (ES
b
= 0.32) improve-
ment in favor of the IK group compared to the IT, and
MBI indicated that IK had a likely (85%) more beneficial
increase in dominant side rotational power compared to
the IT (Table 5). Similarly, both training modalities re-
sulted in improvements in dominant side rotational force
with a large effect (ES
w
= 0.96) for the IK group and a
medium effect (ES
w
= 0.77) for the ITgroup (Table 5). ES
b
statistics together with MBI demonstrated a near small
(ES
b
= 0.19) but likely (MBI = 80%) more beneficial effect
of isokinetic training on dominant side rotational force
compared to isotonic strength training (Table 5). For
dominant side rotational speed both groups increased
with a small (ES
w
= 0.45, IK) to medium (ES
w
= 0.5, IT)
improvement. However, any difference between groups
was considered none to small (Table 5).
Results for force, velocity and power in the non-domi-
nant side rotations were less clear compared to the dom-
inant side. Both the IK and IT groups had medium to
large improvements in force and power, but in velocity
the IT group increased more compared to the IK group
(ES
b
=−0.45; Table 5). MBI statistics, on the other hand,
indicated no clear advantages for either training modal-
ity in any of the non-dominant side rotational variables
force, velocity or power (Table 5).
For lower body power, both groups responded simi-
larly, where the nine-week-training period had no effect
Table 5 Upper body rotational force, power and velocity and lower body power measurements for pre and post training
Pre Mean ±
SD
Post Mean ±
SD
ES
w
ES
b
Magnitude of inference
Harmful Trivial Beneficial
Seated rotation dominant Side
Force 0.19 16% unlikely 4% very unlikely 80% likely
IK (N) 230.0 ± 53.8 287.7 ± 58.1 0.96
IT 224.4 ± 68.5 270.7 ± 48.5 0.77
Power 0.32 14% very unlikely 0% very unlikely 85% likely,
IK (w) 697.5 ± 277.5 942.0 ± 276.4 0.82
IT 581.3 ± 318.5 731.4 ± 278.7 0.5
Velocity −0.11 0% very unlikely 100% most likely 0% very unlikely
IK (m/s) 3.3 ± 0.6 3.6 ± 0.6 0.45
IT 3.0 ± 0.7 3.4 ± 0.7 0.5
Seated rotation non-dominant side
Force (N) −0.10 65% possibly 6% unlikely 29% possible
IK 239.5 ± 52.0 279.3 ± 37.8 0.71
IT 214.9 ± 58.4 260.2 ± 58.4 0.82
Power (W) 0.00 50% possibly 1% very unlikely 49% possibly
IK 725.9 ± 271.9 870.6 ± 247.0 0.5
IT 586.9 ± 310.0 732.8 ± 289.5 0.5
Velocity(m/s) −0.45 0% very unlikely 100% most likely 0% very unlikely
IK 3.28 ± 0.5 3.48 ± 0.7 0.32
IT 2.89 ± 0.7 3.36 ± 0.7 0.79
Lower body
CMJ (cm) −0.11 45% Possible 45% possibly 10% very unlikely
IK 38.2 ± 8.4 38.0 ± 9.1 −0.03
IT 43.1 ± 6.4 43.7 ± 6.6 0.08
LSJ 20 kg (W) 0.02 47% possibly 1% very unlikely 52% possibly
IK 1333.9 ± 209.4 1385.6 ± 227.2 0.22
IT 1288.4 ± 267.5 1335.5 ± 267.5 0.20
SD standard deviation, ES effect size IK isokinetic training group, IT isotonic training group, CMJ counter movement jump, LSJ loaded squat jump, ES
w
within group
ES, ES
b
between group ES
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 7 of 12
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
on CMJ (ES
w
=−0.03 IK and 0.08 IT) and a small effect
on 20 kg loaded squat jumps (ES
w
= 0.22 IK and 0.20 IT)
(Table 5).
Swing kinematics
Results for all measured swing kinematic variables are
presented in Table 6. For a number of variables, includ-
ing shoulder stretch rate (ES
w
= 0.29 for IK and −0.34
for IT), the groups showed different directions of change
(Fig. 1b). After the nine-week training period x-factor
stretch (ES
b
= 0.51), shoulder stretch rate (ES
b
= 0.63),
and arm acceleration (ES
b
= 0.52) had a likely (≥80%)
beneficial effect from isokinetic training compared to
isotonic strength training (Table 6). Furthermore, lead
arm speed had a small increase in both IK (ES
w
= 0.49)
and IT (ES
w
= 0.24) groups, whereas lead arm acceler-
ation had a small increase only in the IK group (ES
w
=
0.48). Comparisons of the two groups showed that
isokinetic training had a likely more beneficial (> 80%)
improvement in lead arm speed and acceleration (ES
b
=
0.24 and ES
b
= 0.52, respectively) compared to isotonic
strength training (Fig. 1c, Table 6).
Driver performance variables
After the nine-week training period, CHS showed no
improvements in neither the IK (ES
w
= 0.17) nor the IT
(ES
w
= 0.18) groups (Table 7). However, both IK and IT
increased ball speed and carry with isokinetic training
showing a small (ES
b
= 0.21) and possible (65%) more
Table 6 Swing kinematics measurements for pre and post training period
Pre Mean ±SD Post Mean±
SD
ES
w
ES
b
Magnitude of inference
Harmful Trivial Beneficial
X-factor (°) −0.41 73% possibly 12% Unlikely 15% Unlikely,
IK 51.2 ± 10.4 48.7 ± 6.1 −0.26
IT 48.3 ± 8.8 49.7 ± 14.7 0.15
X-factor stretch (°) 0.51 4% very unlikely 12% Unlikely 84% Likely
IK 6.9 ± 5.9 8.2 ± 4.2 0.15
IT 10.5 ± 7.1 8.4 ± 8.6 −0.25
X-factor stretch rate (°/s) 0.25 25% possibly 4% very Unlikely 71% possibly
IK 48.4 ± 42.6 48.1 ± 31.7 −0.01
IT 58.3 ± 35.4 48.2 ± 34.3 −0.26
Shoulder stretch (°) 0.67 2% very unlikely 53% possibly 45% possibly
IK 1.6 ± 1.0 2.0 ± 2.3 0.30
IT 1.7 ± 1.7 1.2 ± 2.0 −0.37
Shoulder stretch rate (°/s) 0.63 8% unlikely 4% very unlikely 88% likely
IK 22.4 ± 13.2 26.8 ± 24.2 0.29
IT 18.6 ± 17.3 13.5 ± 19.1 −0.34
Lead arm speed (°/s) 0.24 10% unlikely 2% very unlikely 88% likely
IK 1016.2 ± 96.9 1073.8 ± 96.2 0.49
IT 1012.8 ± 139.5 1042.4 ± 139.6 0.25
Lead arm acceleration (°/s
2
) 0.52 7% unlikely 0% very unlikely 93% likely
IK 5217.0 ± 943.7 5746.2 ± 658.1 0.48
IT 5441.3 ± 1278.4 5403.5 ± 1568.3 −0.03
Thorax speed (°/s) 0.12 29% possibly 4% very unlikely 67% Possibly
IK 697.1 ± 75.4 716.3 ± 53.9 0.28
IT 709.3 ± 67.3 720.1 ± 77.2 0.16
Thorax acceleration (°/s
2
) 0.25 29% possibly 0% very unlikely 71% possibly
IK 3228.8 ± 595.0 3302.2 ± 447.3 0.1
IT 3440.3 ± 636.2 3327.8 ± 873.9 −0.14
Pelvis speed (°/s) 0.14 32%% possibly 4% very unlikely 64% possibly
IK 441.2 ± 68.2 464.1 ± 61.7 0.38
IT 454.2 ± 54.4 468.9 ± 61.4 0.24
Pelvis acceleration (°/s
2
)−0.07 55% possibly 0% very unlikely 45% possibly
IK 2022.3 ± 269.5 2162.5 ± 439.8 0.29
IT 1877.3 ± 640.2 2053.0 ± 801.2 0.36
SD standard deviation, ES effect size, Kisokinetic training group, IT isotonic training group, ES
w
within group ES, ES
b
between group ES
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 8 of 12
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
beneficial effect on ball speed when compared to IT and
a medium (ES
b
= 0.59) likely (78%) more beneficial effect
on carry distance when compared to IT (Fig. 1d,
Table 7).
Discussion
The main findings of this study are that both isokinetic
and isotonic strength training over a 9-week period had
a moderate to large effect on improving rotational
power, force, and velocity in pre-elite golfers. However,
with isokinetic training rotational power and force im-
proved more compared to isotonic strength training,
whereas speed improved to a similar degree in the two
groups. Interesting findings for swing kinematics in-
cluded the between-group differences in X-factor, X-fac-
tor stretch, thorax acceleration, shoulder stretch, and
shoulder stretch rate. The larger improvements seen
with isokinetic training in rotational power and utilisa-
tion of SSC characteristics translated into a higher ball
speed, but not into higher CHS, when compared to
isotonic strength training.
Changes in force velocity and power
Many methods exist for increasing muscular force,
velocity, and power. We chose to investigate the effects
of performing a functional exercise simulating the golf
swing using isokinetic training, an area less investigated.
Both the IK and IT group improved dominant side
rotational force, power, and velocity but IK had a
likely (80–85%) larger improvement in force and
power compared to IT group. No previous studies
have investigated multi-joint isokinetic training in golf
performance but results from a recent study using
the same isokinetic device found that isokinetic lower
body training in different team sport athletes resulted
in superior jump and sprint performance when com-
pared to isotonic training [27]. Another study looking
at upper-body multi-joint isokinetic training in
beginners compared to a non-exercising control
group, found significant increases in select upper
body exercises in the isokinetic group [29]. Isokinetic
training has been proposed to increase the number of
motor neurons recruited and produce a more syn-
chronous firing of motor neurons than dynamic train-
ing alone [41]. The ability to generate maximal
muscular power is considered the most important
neuromuscular function in sports performance [42,
43] and the isokinetic training performed by the IK
group likely (85%) had a beneficial effect on their
dominant side rotational peak power. Previous re-
search comparing effects of resistance training among
men and women suggest that, whilst men show
greater absolute strength and power, both recreational
and elite male and female athletes respond in a simi-
lar way to resistance training and power training pro-
grams [44–46].
Changes in kinematics
Improved knowledge of different physical training
methods, their importance and impact on the golf swing
may allow for a more efficient use of training time. This
study implemented only two training exercises into the
regular training program of the IK group, one of which
was a golf-specific isokinetic rotational movement aimed
to mimic the ballistic movements in the golf swing and
improve driver performance. Our results presented mod-
erately sized between group differences (ES
b
) for x-factor
(0.41), x-factor stretch (0.51), thorax acceleration (0.25),
shoulder stretch (0.67), and shoulder stretch rate (0.63) in
support of isokinetic training. Further analysis of SSC
characteristics showed that IT generally worsened slightly
at both the torso and shoulder whilst the IK group showed
improvement at the shoulder whilst maintaining SSC
parameters in the trunk. Our results for the IT group
where small decreases in several swing kinematic variables
Table 7 Pre and post training period measurements of club head speed, ball speed, and carry distance
Pre Mean ±
SD
Post Mean
±SD
ES
w
ES
b
Magnitude of inference
Harmful Trivial Beneficial
Carry distance (m) 0.31 16% unlikely 6% unlikely 78% likely
IK 197.2 ± 28.6 213.2 ± 34.4 0.59
IT 212.7 ± 24.8 220.4 ± 23.3 0.28
Ball speed (m/s) 0.21 4% very unlikely 32% possible 65% possible
IK 63.4 ± 7.6 65.6 ± 6.6 0.32
IT 65.6 ± 6.7 66.3 ± 6.4 0.11
Club head speed (m/s) −0.01 9% Unlikely 84% Likely 7% Unlikely
IK 46.1 ± 4.4 46.9 ± 4.2 0.17
IT 46.8 ± 5.0 47.7 ± 4.4 0.18
SD standard deviation, ES effect size, IK isokinetic training group, IT isotonic training group, ES
w
within group ES, ES
b
between group ES
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 9 of 12
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
(ES
w
0.25–0.34) were found was rather unexpected since
the IT group did improve force, power, and speed in
addition to maintaining CHS and BS. The reason for this
decrease is difficult to explain but may highlight that
a number of different swing techniques are able to
maintain CHS and BS. Nevertheless, previous research
has shown that increases in strength and power
through isotonic training can influence swing kine-
matics (mechanics) including changes in thorax vel-
ocity [21] and x-factor stretch rate [21] and these
findings support our results for the IK group, but not
for the IT group. Our results demonstrate isokinetic
and isotonic strength training programs can modify
swing kinematics differently, and IK training appears
to be superior for maintaining or improving SSC
characteristics among pre-elite golfers with previous
experience of isotonic training methods.
Changes in driver performance
Our results revealed that isokinetic training may have a
beneficial effect on carry distance and ball speed,
whereas CHS showed no change over the training period
for either group. The isotonic training group in the
current study saw no increase in either CHS or ball
speed, and only a small (ES
w
= 0.28) increase in carry
distance. This is in contrast to strength and plyometric
intervention studies on recreational golfers where im-
provements in CHS, ball speed or driving distance have
been found [16–19]. However, it is well documented that
eliciting changes amongst an elite population is more
difficult [21] and the negligible change in ball speed
(1.1%) and CHS (1.9%) found amongst the IT group are
similar to findings by Doan et al. [21] who reported a
trivial increase of 1.6% in CHS among intercollegiate
level golfers after 11 weeks of strength training. Pre-elite
golfers with a history of strength training, as in our
study, may have already adapted to isotonic training
methods and further isotonic training may not elicit fur-
ther improvements in driver performance.
All participants in this study had an extensive back-
ground in isotonic strength training and plyometric train-
ing, but little to no prior experience of isokinetic training.
The isokinetic group increased in carry distance (7.6%)
with no change in CHS (1.7%), which is similar to Fletcher
et al. [16] results who also found a greater increase in
carry distance (4.3%) compared to CHS (1.5%) from
weight and plyometric training among good club golfers
with very little prior strength and conditioning experience.
We cannot exclude the possibility that the training adapta-
tionsseeninourstudyareinpartduetoanunaccustomed
exercise modality. Nevertheless, we show that isokinetic
training elicits additional responses in golfers already well
adapted to plyometrics and isotonic training. This is similar
to a previous multi-joint isokinetic intervention study in
athletes with considerable experience in strength and
power training [28]. Carry distance and ball speed are not
only dependent on club head velocity, but also centered-
ness of impact, and clubface orientation [4, 5]. An explan-
ation for the improvement in ball speed and carry distance
in the IK group could be that their greater lead arm accel-
eration resulted in reaching lead arm peak speed earlier in
the downswing which may allow for improved centered-
ness of impact, clubhead path, or clubface orientation at
impact. Our results reported increased force development
characteristics in both a seated rotation test for power and
in the golf swing, possibly suggesting that this increase may
transfer into improved centeredness of impact or clubface
orientation at impact, greater ball speed, longer carry dis-
tance and improved driver performance.
In the current study we included a reference group of
highly skilled golfers to account for natural occurring
changes in performance during this training period,
using an open trial method design, which permitted the
participants to self-select experimental group to allow
for international competition schedules; both the IK and
IT groups had average handicaps better than scratch.
There are some uncontrolled variables that may have in-
fluenced the training adaptations; for example, the
current study did not investigate load and intensity of
the normal pre-season training regimens. Both these var-
iables are well known to influence strength and power
training adaptations [14, 28]. Furthermore the individua-
lised pre-season training programs or technical swing
changes could influence results and should be investi-
gated in future studies. Analyses of the change in size of
standard deviation can help describe the change in
homogeneity of a group. For instance the IK group
showed a decrease in size of standard deviation in pre to
post X-factor whilst the IT groups’standard deviation
showed the opposite trend. This suggests that despite
individualised training program and different coaches for
each participant the IK group became more similar after
the training period.
Finally, both IK and IT groups were mixed sexes, and
previous cross-sectional studies [24–26] have shown
some significant differences in swing kinematics between
male and female golfers. In our study we did not find
sex-differences in the pelvis, thorax and shoulder kine-
matic variables before the start of the 9-week training
period. Zheng et al. [26] found differences between men
and women in maximum velocity of the wrists, right
elbow extension, timing of left wrist extension velocity.
However, in line with our findings pelvis, trunk, and left
arm shoulder abduction angles and velocity were found
to be similar between the sexes [26]. Recent research has
reported similar improvements in force and rate of vel-
ocity development between men and women after iso-
kinetic training [48], which is in line with previous
Parker et al. BMC Sports Science, Medicine and Rehabilitation (2017) 9:21 Page 10 of 12
Content courtesy of Springer Nature, terms of use apply. Rights reserved.
research on isotonic resistance training. However, there
is a paucity of research investigating change in swing
kinematics among golfers and even fewer studies com-
paring change in swing kinematics between men and
women, an area in need of further investigation.
Conclusion
Isokinetic training among pre-elite golfers with a history
of strength and conditioning training increased rota-
tional power development, SSC characteristics around
the shoulder, lead arm peak speed, ball speed, and carry
distance more compared to isotonic training. Even
though isokinetic training did not increase CHS, it did
result in greater carry distance and thus improved driver
performance.
Abbreviations
CHS: Club head speed; CMJ: Countermovement jump; ES
b
: Between-group
effect size; ES
w
: Within group effect size; IK: Isokinetic power training group;
IT: Isotonic strength training group; MBI: Magnitude-based inference;
SSC: Stretch-shortening cycle
Acknowledgements
We are grateful to the participants who volunteered in the study.
Funding
This study was supported by the Knowledge Foundation (KK-stiftelsen) of
Sweden under Grant 2012/0319 to MCO. The KK provided the funding for
the present study but was not involved in the analysis, interpretation or the
right to approve or disapprove publication of the research.
Availability of data and materials
The datasets used and analysed during the current study are available from
the corresponding author on reasonable request.
Authors’contributions
JP was responsible for the original study design and contributed to all parts
of the work of this study. CL was involved in the data collection, data
analysis, and manuscript preparation. MCO was involved in the study design,
data analysis, and manuscript preparation. MCO,
JP, and JH were involved in the theoretical conceptualization and in the
interpretation of the study data. All authors commented on the draft, read
and approved the final manuscript.
Ethics approval and consent to participate
This study was approved by the Regional ethics committee in Lund, Sweden
(Dnr 2016/12) and all the participants provided written consent to
participate in the study.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Publisher’sNote
Springer Nature remains neutral with regard to jurisdictional claims in
published maps and institutional affiliations.
Author details
1
The Rydberg Laboratory for Applied Sciences, School of Business,
Engineering and Science, Halmstad University, Box 823, 301 18 Halmstad,
Sweden.
2
Scandinavian College of Sport, Box 11365, 494 28 Gothenburg,
Sweden.
3
Swedish Golf Federation, Stockholm, Sweden.
Received: 26 May 2017 Accepted: 30 November 2017
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