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ORIGINAL ARTICLE
An ergonomic comparison of rowing machine designs:
possible implications for safety
I A Bernstein, O Webber, R Woledge
.............................................................................................................................
Br J Sports Med
2002;36:108–112
Objectives: Ergometer training is a common cause of injuries in rowers. A randomised crossover study
comparing two power head designs was carried out to examine ergonomic risk factors.
Methods: Six elite male rowers undertook 20 minute fatiguing rowing pieces with both fixed and float-
ing power heads. A CODA MPX infrared telemetric motion analysis detector and the ergometer’s inter-
face were used to measure displacement, force, work performed, and power output.
Results: There was no significant difference in the total work performed, power per stroke, or
metabolic load between the two ergometer designs. Fatigue was shown by a mean (SEM) fall of 9.7
(0.79) W/stroke (95% confidence interval (CI) 8.0 to 11.5) between minutes 8–10 and minutes 16–18
(p<0.001). The stroke length was 53 (13) mm (95% CI 18 to 89) longer with the fixed power head
(p<0.02). With fatigue, the stroke with the fixed power head lengthened at the “catch” (beginning of
the stroke) by 19.5 mm (p<0.01) and shortened at the finish of the stroke by 7.2 mm (p<0.05). No sig-
nificant changes in stroke length were seen with the floating power head. The mean force per stroke
was 12.1% (95% CI 3.0 to 21.2) (27.3 (8.0) N) higher with the power head fixed versus floating
(p<0.02).
Conclusions: It is postulated that longer stroke lengths and greater forces are risk factors for soft tissue
injuries. Further research into whether floating power head rowing ergometers are associated with
lower injury rates than fixed power head designs is now needed.
E
rgometer training on rowing machines has been thought
by elite rowers to be a common cause of land training
injuries, particularly back injuries.
1
It is still not known
whether low back pain occurs more often in rowers than the
general population. In elite rowers, more than 50% of injuries
occurred off the water during land based training.
12
Injuries in
rowing are rare events (1 per 1000 hours) compared with
other sports.
2
However, when they do occur, they cause elite
rowers to lose an average of 24 days of training a year
1
often
preventing selection for the national teams.
2
At the elite level,
training sessions on most days of the week involve continuous
rowing on the water for 60–90 minutes at intensities just
below the anaerobic threshold.
3
Ergometers are often used for
training and assessing rowers. In these rowers, land based
training carries a 10-fold higher risk of injury per hour than
water based training,
2
the leading causes suggested being
weights and ergometer training.
1
Stationary rowing ergometers (fixed power head designs)
are the most commonly used type in this country. Other
designs are based on mounting the whole ergometer on
wheels (wheeled ergometer) or mounting the power head on
rollers so that it can move independently of the seat on the
slide track (floating power head design). The mechanical
characteristics of these designs have been compared.
45
Float-
ing power head and wheeled ergometer designs more closely
simulate the mechanics and kinetic energy characteristics of
rowing on the water than do stationary ergometers.
45
However, these studies did not examine risk factors for
injuries.
In repetitive lifting, an action similar to rowing, muscle
fatigue rather than primary failure of passive structures was
the most important factor leading to instability of the spine.
6
A substantial part of the bending moment in the flexed spine
was resisted by passive structures as muscles fatigued with
repetitive lifting.
7
Gradual disc prolapse is an injury reported
in rowers.
8
Perhaps this is a result of repetitive lumbar flexion
under load because this was shown to lead to gradual disc
prolapse in a cadaveric study.
9
Fatigue has been shown to lead
to loss of coordination in rowers on the water.
10
However, there
has been no published work on the relation between fatigue,
coordination, and injury on rowing ergometers.
We therefore conducted a randomised crossover study to
examine the ergonomic differences between two commonly
used rowing ergometer power head designs. The trial design
allowed us to study the effects of fatigue as well as account for
the large variation between subjects.
METHODS
Study population
Six elite male oarsmen as classified by the Amateur Rowing
Association
11
(mean age 30 (range 22–40); mean (SD) height
1.87 (0.07) m; mean (SD) mass 80 (11) kg) volunteered for the
study. Exclusion factors were: a history of serious injury,
recent illness, and inexperience on the rowing ergometers
used. Prior ethical approval was granted from the Royal
National Orthopaedic Hospital Trust ethics committee. Signed
consent was obtained from each subject.
Equipment and methods
The subjects each performed two 20 minute rows on a
RowPerfect rowing ergometer (Care RowPerfect BV, JV Hard-
enberg, The Netherlands) in the laboratory. This ergometer
has a “floating” power head—that is, the footplate with the
power head unit and the seat are both mounted on the slide
track and are thus free to move independently (fig 1). The
mass of the power head (about 17 kg) is similar to that of a
section of a boat containing one oarsman. To simulate a fixed
power head ergometer, the floating head was clamped at one
end. The chain was placed on the larger of two cogwheels, and
a 39 cm disc was used to set the resistance on the fly wheel for
all pieces. The display settings were set to simulate a coxless
four boat type. A Polar surface chest monitor and telemetric
sensor was connected to the ergometer interface. The ergom-
eter interface provides force data, sampled every 20th stroke,
See end of article for
authors’ affiliations
.......................
Correspondence to:
Dr Bernstein, Gordon
House Surgery, 78 Mattock
Lane, London W13 0NZ,
UK; ibernstein@
gordonhouse.freeserve.co.uk
.......................
108
www.bjsportmed.com
derived from measurement of the speed of the flywheel. The
accuracy and repeatability obtained from comparison with a
calibrated force plate was ± 0.1%.
The subjects were randomised (without replacement) into a
crossover study design so that half started with a fixed power
head and the other half with a floating power head. The sub-
jects stretched and warmed up on the ergometer for at least 10
minutes before each row. A break of at least 45 minutes
between the two pieces was given for rest and rehydration
while the power head was changed. The subjects were given a
minimum pulse rate to maintain during the pieces, to ensure
that they were exercising above their anaerobic thresholds and
developed fatigue. This was determined by previous physio-
logical testing at the British Olympic Medical Centre,
including measurement of capillary blood lactate levels. The
subjects were asked to use the first several minutes to achieve
the target pulse rate and then to keep the pulse rate steady.
Displacements were measured by a CODA MPX motion
analysis system (Charwood Dynamics Ltd, Rothley, Leicester-
shire, UK) using infrared active markers fixed to the subjects’
skin or to the ergometer by adhesive tape. Twenty one markers
were in fact used, but only data from markers on the handle
and footplate are reported in this paper. Three dimensional
coordinates were obtained for each marker at 100 Hz. The
standard deviation of repeated measurements was less than
0.2 mm, and the accuracy obtained from a calibration grid was
± 0.3 mm. Forty second samples of rowing were taken every
two minutes. Each acquisition period was divided into stroke
cycles. Each cycle was defined by the maximum horizontal
displacement of the handle with respect to the footplate. This
defined the beginning of the stroke (“the catch”). Incomplete
cycles at the beginning and end of the data acquisition period
were discarded. The data were averaged across all of the com-
plete cycles. It was not possible to synchronise data from the
CODA and the ergometer interface, which were therefore ana-
lysed separately.
Fatigue was examined by comparing a time period after the
anaerobic threshold was reached and a period towards the end
of the piece which was not affected by the subjects “sprinting”
to the line. Some data were not obtained successfully.
Therefore the periods for comparison of the ergometer data
were from 8 to 10 minutes and from 16 to 18 minutes,
amounting to two minute samples. The periods for the CODA
data were from 7 to 12 minutes and from 13 to 18 minutes,
each period encompassing three 40 second data acquisitions,
amounting to a total of a two minute sample. The length of the
periods was chosen to include sufficient data for the repeated
measures analysis.
Main outcome measures
The outcome measures recorded from the ergometer interface
were: power output; work performed; force displacement
curves; pulse rate; stroke rate; time elapsed; stroke number.
Stroke length was recorded by the CODA system.
Missing data
The first ten minutes of ergometer data for one subject was
lost as the result of computer failure. The remaining data for
that row was used for the analysis, the sampling periods being
11–13 minutes and 17–19 minutes.
Statistical analysis
Significance tests were based on the paired t test for the effects
of fatigue on the means of the ergometer derived variables.
Normalised peak force data were examined using an unpaired
t test. The CODA derived stroke length data were examined
using two way analysis of variance with replication. A grid of
t tests, as applied to the special case of crossover trials,
12
exam-
ined the differences between the power head design, the order
of the trials, and the interaction between power head design
and trial order. A repeated measures calculation was used
where appropriate. The normality of the data was examined
with a Kolmogorov-Smirnov test.
Statistical power
Statistical significance was defined at the two tailed p = 0.05
level. Confidence limits at the 95% level are presented where
appropriate. The final data set generated more than 85% power
to detect the observed changes in stroke length and
differences in normalised force displacement curves between
the fixed and floating power heads.
RESULTS
Table 1 compares the key characteristics of the subjects in each
group. Table 2A classifies the main ergometer and pulse rate
data by power head design. The same work was performed
with both power heads. Pulse rates were above the target rates
for the second half of each piece. Table 2B classifies the same
data by first versus second pieces. There were no significant
differences in the time to reach target pulse rates or mean
pulse rates during the period from 14 to 19 minutes compar-
ing floating versus fixed power heads or first versus second
pieces.
Subjects showed a mean (SEM) fall of 9.7 (0.79) W/stroke
(95% confidence interval (CI) 8.0 to 11.5) between minutes
8–10 and minutes 16–18 (p<0.001). There was no significant
difference in this fall between the fixed and floating power
heads. Further effects of fatigue were indicated by a fall in
total work and mean power per stroke between the first and
second pieces (table 2B).
Figure 1 Photographs showing rowing movements with the power
head fixed and floating. Courtesy of C. Pekkers.
Table 1 Characteristics of subjects in each group
Characteristic Group 1 Group 2
No of subjects 3 3
Age (years) 28.7 (5.9) 32.7 (6.4)
Height (m) 1.8 (0.03) 1.9 (0.1)
Weight (kg) 77.8 (4.2) 81.9 (16.1)
Target pulse (beats/min) 172.0 (2.7) 170.7 (3.1)
Values are mean (SD) of the group. The significance of the
differences between the groups was tested with Student’s
t
test. No
significant differences were found.
Comparison of rowing ergometer designs 109
www.bjsportmed.com
Stroke length
Analysis of the CODA data showed that the stroke length,
after target pulse rates were achieved, was 53 (13) mm (95%
CI 18 to 89) longer with the fixed than with the floating
power head (p<0.02). In addition to this observation, there
were further changes in the horizontal handle displacement
(stroke length) as the pieces progressed with the fixed power
head only. Specifically, in the horizontal plane, the handle
went further beyond the footplate at the beginning of the
stroke (stroke lengthening at the catch) and also finished
nearer the footplate at the end of the stroke (stroke shorten-
ing at the finish) (table 3A). Comparison of the stroke length
with first versus second piece showed no increase during the
first piece but a small increase during the second piece (table
3B).
Force data
The force versus handle displacement data from the ergometer
interface was sampled every 20th stroke. Figure 2 shows typical
curves for the mean data for one rower. The mean force per stroke
across all the subjects was 12.1% (95% CI 3.0 to 21.2) (27.3 (8.0)
N) higher with the power head fixed versus floating (p<0.02).
To examine the differences in shapes between fixed and
floating heads, the curves were normalised to give them the
same area. This was achieved by dividing each point on the
curve by the mean value for the whole curve. Figure 3 shows
the normalised curves for the same rower as shown in fig 2.
The mean work performed to half of the handle displacement
(the area under the curves to the left of the vertical line in fig
3) was 64.1% of the total work performed with the fixed power
head and 67.8% with the floating power head. The difference
Table 2 Measurements made during rowing pieces from the ergometer interface
Variable Fixed Floating Difference (95% CI) Standard error p Value
(A) Comparison between fixed and floating power heads
Work performed (kJ) 368 365 2 (−8to13) 4 NS
No of strokes 464 506 −42 (−15 to −69) 10 <0.02
Power per stroke (W) 314 308 6 (−11 to 23) 6 NS
Work performed per stroke (J) 813 728 84 (55 to 113) 10 <0.001
Pulse rate: minutes 14–19 (beats/min) 180 183 −3(−7to1) 1 NS
Time to target pulse (s) 449 392 57 (−174 to 287) 83 NS
Variable 1st Piece 2nd Piece Difference (95% CI) Standard error p Value
(B) Comparison between first and second pieces
Work performed (kJ) 371 361 10 (−0.3 to 20) 4 <0.06
No of strokes 477 492 −15 (−42 to 12) 10 NS
Power per stroke (W) 320 301 19 (2 to 36) 6 <0.05
Work performed per stroke (J) 797 744 52 (23 to 81) 10 <0.01
Pulse rate: minutes 14–19 (beats/min) 180 183 −3(−6to1) 1 NS
Time to target pulse (s) 457 385 72 (−158 to 303) 83 NS
Significance is given by two way
t
test analysis. Values are means, differences and standard errors of the differences (95% confidence intervals).
Table 3 Change during the piece in length at each end of the stroke measured by the CODA system
Fixed power head Floating power head
Length change (mm) p Value Length change (mm) p Value
(A) Comparison between fixed and floating power heads
Catch 19.5 (32.6) <0.01 −3.5 (36.3) NS
Finish 7.6 (27.2) <0.05 −4.9 (30.8) NS
First piece Second piece
Length change (mm) p Value Length change (mm) p Value
(B) Comparison between first and second pieces
Catch 7.6 (50.0) NS 8.4 (12.4) <0.001
Finish 2.3 (41.4) NS 0.4 (7.8) NS
Values are the mean differences (SD) between the average displacements during minutes 7–12 compared with minutes 13–18. Positive numbers indicate
movement towards the power head. Significance is given by two way analysis of variance with replication.
Figure 2 Example of the mean force versus handle displacement
plots with the power head fixed and floating for one rower. Data are
averaged over one piece.
600
450
300
0
150
2.0
Handle displacement (m)
Floating power head
Fixed power head
Force (N)
1.51.00.0 0.5
Figure 3 Example of the normalised mean force versus handle
displacement plots with the power head fixed and floating for the
same rower as in fig 2. Data averaged over the whole of one piece.
The area under each curve to the left of the vertical line represents
percentage of total work performed to half of the total handle
displacement.
3
2
1
0
0.5
2.0
Handle displacement (m)
Normalised force
1.51.00.0 0.5
2.5
1.5
Normalised floating average
Normalised fixed average
110 Bernstein, Webber, Woledge
www.bjsportmed.com
was 3.7 (1.2)% (95% CI 0.67% to 6.80%) (p<0.05). In contrast
with the raw data, the peak force was higher in all subjects
with the floating power head (p<0.05). In five out of six sub-
jects, the peak force occurred earlier in the stroke with the
floating power head compared with the fixed power head.
DISCUSSION
Differences between the force displacement profiles on fixed
compared with floating power head rowing ergometers have
been found. The stroke length was longer on the fixed power
head ergometer than the floating power head. The stroke
length increased further, particularly at the catch, with fatigue
on the fixed power head but not the floating power head. The
fixed power head ergometer led to higher mean forces being
developed for the same metabolic load and total work
performed. These differences may increase the risk of injury
when training at submaximal loads on fixed power head
ergometers compared with floating power head ergometers.
Discussion of method
The randomised crossover design reduced the effect of fatigue
being carried over from the first to the second piece. However,
this could be reduced further by performing the pieces on
separate days.
Critical to the design of the study was the need to reproduce
fatigue. Urhausen and colleagues
13
have validated the use of
pulse rates for determining exercise intensity in relation to
blood lactate measurements in rowers, on both the water and
a rowing ergometer. As pulse rate is approximately linearly
related to V
O
2
, we concluded that we had produced adequate
fatigue, above the subjects’ anaerobic threshold, with this pro-
tocol. The subjects invoked a variety of adaptations to
maintain power output in the face of fatigue. In spite of these
adaptations, we still observed a small fall in the power output
per stroke within the pieces.
Work performed
The total work performed over the whole piece was the same
with both power heads, consistent with setting the same tar-
get pulse rates for each piece. The stroke rate was lower and
the work performed per stroke was higher with the power
head fixed (table 2A). This would explain the observed differ-
ence in the areas under the force displacement curves in fig 2,
which represent the mean work performed per stroke. The
power per stroke was defined as the work performed per
stroke divided by the time for each stroke. The difference in
stroke rate accounted for the observation that the power per
stroke was similar with both power heads.
Stroke length and biomechanics
The stroke length was 53 mm longer with the power head
fixed. Following the principle of the conservation of momen-
tum, the kinetic energy of the body in the static case can be
shown to be much higher than the kinetic energy of the body
plus power head in the floating case.
14
The kinetic energy of
the moving masses (given by 0.5mv
2
) has to reduce to zero at
each end of the stroke and is higher by a factor of about 6 (or
about 60 J per stroke) for the fixed power head. The kinetic
energy is likely to be absorbed by muscles working eccentri-
cally to decelerate the moving masses. The work-energy theo-
rem predicts that the distance taken to reduce the kinetic
energy to zero will be further when the kinetic energy is
higher. This is consistent with our observations of longer
stroke lengths with the power head fixed.
The longer stroke lengths with the power head fixed
presents a possible risk factor for injury to the musculotendi-
nous junction.
15
This would be exacerbated by our observation
that fatigue caused further lengthening at the beginning of
the stroke. Lengthening of the back extensor muscles in row-
ers may cause the transference of loads to the posterior
viscoelastic structures of the vertebral units. This has been
observed with fatigue in repetitive lifting studies.
7
If studies of
activation of these muscles confirm their role in decelerating
the body at each end of the stroke (as seen with repetitive
bending
15
), this would provide a plausible link to the produc-
tion of back injuries.
Mair and colleagues
15
showed that fatigue in muscles work-
ing eccentrically resulted in a reduction in their ability to
absorb kinetic energy and an increase in their length before
being irreversibly damaged. This may explain the increase in
stroke length with fatigue that was observed with the fixed
power head. When muscles are working eccentrically, a
smaller proportion of the fibres are active than when the same
force is developed concentrically.
16
Therefore the force is
distributed across fewer fibres leading to a greater stress (force
per unit area), which is potentially damaging.
Force displacement curves
Our normalised force displacement curves (fig 3) concord with
the findings of Hänyes and Lippens.
17
They show that the force
on the handle rose later with a fixed power head ergometer
compared with the forces in a boat, similar to our comparison
between fixed and floating power heads. Rekers
4
showed directly
that the force displacement curves were very similar in size and
shape when a floating power head was compared with a boat.
4
In fig 2, the mean forces developed during the power phase
were significantly higher with the power head fixed. As
fatigue developed, some of these forces could be transferred to
passive viscoelastic structures (tendons, ligaments, cartilage,
and intervertebral discs) leading to permanent deformation.
7
Theoretical calculations have shown that the forces within the
body may vary by much greater amounts than those observed
on the handle in changing the power heads.
4
Therefore there
may be a higher chance of injury with the power head fixed.
The earlier increase in force development during the stroke
with the power head floating (fig 3) was predicted from theo-
retical considerations.
414
With the power head fixed compared
with floating, much of the initial force developed on the foot-
plate would be dissipated in accelerating the whole body mass
before that force could appear on the handle.
Further study
Further analysis of our data will allow us to calculate the kinetic
energy of the system to test the theoretical arguments above.
Future work using this experimental setup could yield
information about changes in coordination and accessory move-
ments with fatigue to identify further risk factors for injury.
Conclusion
The reduction in injury risk obtained by using floating power
head ergometers instead of fixed power head ergometers can-
not be quantified here. However, given the trend towards low
intensity long distance training, we would expect further
research to find that changing to floating power head ergom-
eters would reduce injuries attributable to ergometer training.
ACKNOWLEDGEMENTS
IB was funded by a Department of Health grant as part of the funding
towards an MSc in musculoskeletal medicine and osteopathy at Uni-
versity College, London. The manufacturer of the ergometer has
posted photographs comparing the fixed and floating power heads at
www.rowperfect.com
Take home message
The stroke length is longer and the mean forces are higher
on fixed compared with floating power head ergometers.
This could increase the risk of injury. Therefore direct
research into injury rates with the different ergometers
would be very desirable.
Comparison of rowing ergometer designs 111
www.bjsportmed.com
.....................
Authors’ affiliations
I A Bernstein, O Webber, R Woledge, UCL Institute of Human
Performance, Royal National Orthopaedic Hospital Trust, Brockley Hill,
Stanmore, Middlesex HA7 4LP, UK
Conflicts of interest: The ergometer was donated to the laboratory by the
manufacturer who was approached only after the design of the project
and the testing protocol had been established.
REFERENCES
1 Bernstein IA. Injury reporting system in rowing.
Proceedings of the
Senior Coaches Conference
. London: British Amateur Rowing
Association, 1994.
2 Budgett RGMcB, Fuller GN. Illness and injury in international oarsmen.
Clin Sports Med
1989;1:57–61.
3 Hartmann U, Faulmann L, Altenburg D,
et al
.
Proceedings of the Senior
Coaches Conference
. London: British Amateur Rowing Association,
1992.
4 Rekers C. Verification of the RowPerfect rowing ergometer.
Proceedings
of the Senior Coaches Conference
. London: British Amateur Rowing
Association, 1993.
5 Martindale WO, Robertson DGE. Mechanical energy in sculling and in
rowing an ergometer.
Can J Appl Sport Sci
1984;9:153–63.
6 Gardner-Morse M, Stokes IAF, Laible JP. Role of muscles in lumbar
spine stability in maximum extension efforts.
J Orthop Res
1995;13:802–8.
7 Sparto PJ, Parnianpour M, Reinsel TE,
et al
. The effect of multijoint
kinematics and load sharing during a repetitive lifting test.
Spine
1997;22:2647–54.
8 Stallard M. Back injuries in rowing: the surgeon’s contribution.
Proceedings of the Senior Coaches Conference
. London: British Amateur
Rowing Association, 1994.
9 Adams MA, Hutton WC. Gradual disc prolapse.
Spine
1985;10:524–31.
10 Wing AM, Woodburn C. The coordination and consistency of rowers in
a racing eight.
J Sports Sci
1995;13:187–97.
11 British Amateur Rowing Association.Rulesofracing.
The Almanac.
London: British Amateur Rowing Association, 1999.
12 Armitage P, Berry G.
Statistical methods in medical research.
3rd ed.
Oxford UK: Blackwell Sciences, 1994:245–9.
13 Urhausen A, Weiler B, Kindermann W. Heart rate, blood lactate and
catecholamines during ergometer and on water rowing.
Int J Sports Med
1993;14:20–3.
14 Dudhia A. FAQ: the physics of ergometers. http://www.atm.ox.ac.uk/
rowing/physics.html. Updated 15/2/99.
15 Mair SD, Seaber AV, Glisson RR,
et al
. The role of fatigue in
susceptibility to acute muscle strain injury.
Am J Sport Med
1996;24:137–43.
16 de Looze MP, Toussaint JH, van Dieën JH,
et al
. Joint movements and
muscle activity in the lower extremities and lower back in lifting and
lowering tasks.
J Biomech
1993;26:1067–76.
17 Hänyes VB, Lippens V. Vom Messen im Boot und auf dem
Ruderergometer.
Rudersport
1988;30:10–14.
BASEM 2002 CONGRESS .............................................................................
The Aircast Travelling Fellowship 2002
T
he Fellowship, funded by Aircast Limited Partnership is open to Medical Practitioners under the age
of 40 years, as of 1 November 2002, for unpublished original work relevant to sport and exercise
medicine.
The work should include a structured abstract and be presented in the standard format of introduction,
methods, results, discussion, conclusion, references, and should include acknowledgement of support
received. The abstract should be approximately 250 words and the body 5000 words. Submissions should
be posted to the address below to arrive no later than 1 August 2002.
The fellowship will allow the holder to spend two weeks in a medical centre of excellence anywhere in
the world appropriate to the award holder’s interests. Receipted expenses including the airfare will be
awarded to a maximum of £2000.00. The holder will be expected to give a 20 minute presentation of his
or her work, as submitted, at the BASEM Annual Congress at The Low Wood Hotel, Windermere on Fri-
day 11 October 2002, at 5.45pm.
Dr I D Adams
British Association of Sport and Exercise Medicine,
25 Parish Ghyll Drive, Ilkley, Yorkshire,
LS29 9PT, UK
Please vist the
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portion of our
website www.
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for the full
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112 Bernstein, Webber, Woledge
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