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rowing experience. Conclusion: a consistent sequence of peak muscle activity and RC was found,
with RC following OEA activity closely. This indicates that the ribs may undergo compressive
Obliquus Externus Abdominis [OEA]) as cadavers. Most fatigue fractures produced were
*c 2000 Harcourt Pub
Henry Wajswelner,
Kim Bennell,
Ian Story,
Joan McKeenan
School of
Physiotherapy,
Faculty of Medicine,
Dentistry and
Health Sciences,
The University of
Melbourne,
Parkville Victoria
3010, Australia
Correspondence to:
Henry Wajswelner.
Tel: ‡61393444171;
Fax: ‡61393444188;
E-mail: h.
wajswelner@physio.
unimelb.edu.au
possible sources of muscular stress to the ribs in
rowing (Holden & Jackson 1985; Hosea et al.
1989; McKenzie 1989; Wajswelner 1991; Boland
& Hosea 1994; Gaffney 1997). Most of these
reports cite the antero-lateral aspect of the
ribcage between the fourth and eighth ribs to be
a common site for this injury (Wajswelner
1996).
found in the posterolateral parts of the sixth or
seventh ribs, not antero-laterally at the site of
SA muscle attachment. This suggests that SA
activity alone may not be the mechanism of
antero-lateral rib stress fractures in rowers.
Karlson (1998) examined the cause of rib
stress fractures in elite rowers with a
retrospective review of 14 fractures in
stressing via OEA activity rather than SA activity in rowing. # 2000 Harcourt Publishers Ltd
Introduction
Stress fractures of the ribs are one of the most
serious injuries sustained by participants in the
sport of rowing, with an injury rate reported as
ranging from 5±20% (Wajswelner et al. 1995;
Hickey et al. 1996). Rib stress fractures have
been reported in elite, club and school levels of
rowing and are reported to cause the most time
lost due to injury (Coburn et al. 1993).
Previous authors have identi®ed the muscles
of the chest wall (Serratus Anterior [SA] and
McKenzie (1989) reported a case of a stress
fracture of the ninth rib in an elite oarsman, and
postulated that the cause was SA acting to
protract the scapula during the recovery phase
of the stroke.
Using in vivo and in vitro designs, Satou and
Konisi (1991) investigated the mechanism by
which the SA muscles might cause a rib stress
fracture. Electromyography (EMG) data from
human subjects were used to estimate three-
dimensional resultant forces, which were then
reproduced and applied to the ribs of fresh
Muscle action an
ribs in rowing
Henry Wajswelner, Kim Bennell, Ian
Objective: chest muscle action has been propose
objective was to examine the sequence of peak c
ribcage compression during the rowing stroke. D
was used. Subjects and Setting: seventy-four row
school levels of competition were tested at the A
School of Physiotherapy at the University of Mel
measure timing of peak activity of serratus ante
An extensometer indicated the time of maximal
ergometer and the sequence of these events was
before the catch while OEA peak activity occurre
closely, and was not coincident with peak SA ac
Original Research
Holden and Jackson (1985) stated that SA is
one of the major contributors to bending stress
across the ribs, and that movement involving
the SA could exert signi®cant stress to the ribs.
lishers Ltd
d stress on the
Story and Joan McKeenan
as a cause of rib stress fractures in rowers. The
est muscle electromyography (EMG) activity and
sign: a within-groups, repeated measures design
rs (34 male, 40 female) from elite, club and
ustralian Institute of Sport in Canberra or the
ourne. Method: surface EMG was used to
or (SA) and obliquus externis abdominis (OEA).
bcage compression (RC). Subjects used a rowing
xamined. Results: SA peak activity occurred just
at the ®nish of the stroke. RC followed OEA
vity. Results were consistent across the levels of
10 patients. He concluded that there was a
similarity in site between the rib stress
fractures caused by rowing and those caused
by coughing, implying that the OEA muscles
Physical Therapy In Sport (2000) 1, 75±84 75
play a signi®cant role in the mechanism of
injury.
There is, therefore, a need to de®ne the role of
the SA and the OEA muscle in the development
of rib stress fractures in rowing. To date, no
study has attempted to link the activity of these
mu
the
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ph
aim
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between peak activity of these muscles,
me
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and timing of maximal ribcage compression in
the
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Su
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gro
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gro
competition and experience in rowing. To be
included in the study, subjects had to be
familiar with the use of the rowing ergometer
and currently free of injury. Table 1 provides a
summary of subject characteristics.
Seventeen of these subjects had a previous
is
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en
e
13
nd
e
ro
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u
g
o
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re¯
han
lumination. The image of this ball was later
sed to time-normalize and divide the stroke
t
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76 Physical Therap
Physical Therapy in Sport
Tab
Gro
Oar
Gen
Hea
Ligh
Tot
Swe
rowing stroke. The project used a repeated
asure, within groups design so that
iability of measurement could also be
mined.
bjects
bjects were a convenience sample of 74 (34
40 F) active rowers from three representative
ups within the Australian rowing
munity: elite (international competitors),
b (national), and school groups. The three
ups re¯ected three distinct levels of
il
u
in
1
N
ch
m
el
el
A
H
A
le 1 Subject numbers in different categories
up Elite: 24 Club: 21
Sweep: 15 Scull: 9 Sweep: 12
der M F M F M F
asured with surface electromyography
MG) and maximal ribcage compression,
asured with an extensometer, was examined
ring the rowing stroke.
ethod
ics approval for this study was obtained
m The University of Melbourne Human
search Ethics Committee.
he outcome measures were timing of peak
scle activity for the SA and the OEA muscles
a
th
P
S
ro
er
(C
T
w
scles with compression of the ribcage during
rowing stroke. The portion or phase of the
ke in which the ribs are maximally
pressed is unknown, so it is dif®cult for the
ysical therapist to offer useful clinical advice
ed at preventing stress to the ribcage in
ing.
n this project, the temporal relationship
h
b
to
th
th
ca
T
w
y in Sport (2000) 1, 75±84
vy 7 6 2 4 6 4
t 2 0 3 0 2 0
al 9 6 5 4 8 4
ep: Single oar rower; Heavy: heavy weight category; Scull:
o phases.
EMG was acquired with the Amlab system
7 (Associative Measurement P/L, Lane Cove,
W, Australia). There were four SEMG input
nnels, one each for both SA and OEA
scles. Each channel had two active
ctrodes, and there was one common ground
ctrode. The electrodes used were paediatric
/AgCl (Red Dot, model No. 2258-3, 3M
alth Care, St Paul, Minnesota, USA).
plication of the SEMG electrodes was
School: 29
Scull: 9 Sweep: 29 Scull: 0
M F M F M F
tory of rib stress fractures, con®rmed on
ne scans, and another ®ve subjects went on
develop rib stress fractures after testing. Of
se 22 stress fracture cases, 12 (50%) were in
elite category, seven (33%) in the club
egory and three (10%) in the school category.
(18%) were sweep rowers and 12 (66%)
re scullers. There were nine (26%) males and
(32%) females, with 14 (22%) heavy weight
eight (73%) light weight rowers sustaining
injury.
cedures
bjects performed a standardized stretching
tine and a warm-up on a Concept II rowing
ometer identical to the one used to testing
ncept P/L, Morrissville, Vermont, USA).
e rowing trials were videotaped and tapes
re time-encoded. A 3.0 cm diameter
ective ball was taped to the side of the oar
dle and two ¯oodlights were used for
*c 2000 Harcourt Publishers Ltd
32 9 20 0 0
0 4 0 0 0 0
3 6 9 20 0 0
Two oar rower; Light: Light weight category.
correlation of length to output was excellent
(r2 ˆ 0.96). RR data were acquired with the
SEMG data via the Amlab system.
SEMG processing
The raw signals were ampli®ed and passed
through a second order quasi-Butterworth high
pass ®lter set at a corner frequency of 20 Hz,
attenuating frequencies below the corner
frequency at a rate of 12 dB/octave. The signal
was full wave recti®ed and smoothed by
peak detection with attack and decay time
constants set at 50 ms, to produce a linear
envelope.
All data were originally sampled at 1000 Hz;
*c 2000 Harcourt Pub
M
Fig. 1 Rubbery ruler positioned at back of chest and
method of taping over chest band.
performed with subjects supine, directly after
warm-up and stretching. The skin was prepared
by wiping with an alcohol swab. The correct
location for placement of the electrodes was
determined using a hand-held EMG scanning
device (Myotrac, model number 4001,
Thought Technology Ltd., West Chazy, New
York, USA).
SEMG electrodes were applied to the SA at
the antero-lateral aspects of the ribcage. Prior to
application of the test electrodes, subjects were
asked to protract one scapula by stretching the
arm up vertically while the Myotrac was
applied to locate the site. The electrodes were
positioned at the point in the muscle where the
most signal could be obtained during the
protraction. Two electrodes were placed along
the length of the same digitation of SA with an
approximate inter-electrode distance of 0.5 cm.
The same procedure was used to place
electrodes on the OEA muscles, located and
con®rmed with an isometric abdominal hold
using a half sit-up to activate the OEA.
One common electrode was placed over a
prominent spinous process on the upper
lumbar spine near the thoraco-lumbar junction
(Fig. 1). The subject was then positioned on the
rowing ergometer for application of the
extensometer.
The extensometer or rubbery ruler (RR) was
used to measure change in circumference of the
ribcage. Developed by the Physics Department
of The University of Melbourne, it is a length of
silicone rubber containing two copper wires
coiled like a double helix. In its unstretched
state, the RR output is zero mV. When stretched
it does not measure strain but can instantly
measure length to a very high resolution
(10ÿ6 m).
The RR was 10.4 cm in its unstretched state
and was glued each end to velcro tabs. These
were adhered to the ends of a rigid fabric band,
which was passed around the chest of the
subject. At the front of the chest the band was
passed through a plastic ring taped to the
sternal area. The RR was positioned at the back
of the subject's chest as shown in Figure 1. The
band was secured postero-laterally with
strapping tape to allow it to slide horizontally
(Fig. 1).
Before use the RR was calibrated to correlate
output values in mV with length in cm. The
lishers Ltd
uscle action and stress on the ribs in rowing
this was reduced by decimation by a factor of
20 to match the frequency of video frames. Thus
each video frame had corresponding SEMG and
RR values (50 samples per second).
Physical Therapy In Sport (2000) 1, 75±84 77
Checking for Crosstalk
Th
vol
(sc
¯ex
T
the
sig
wa
U
acquisition was corrected by re-positioning the
ele
He
art
elim
on
the
Tim
sys
A
po
tim
Am
sim
sys
L
®rst visible on the videotape was identi®ed and
ma
all
the
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ma
eac
Ro
Th
20
mi
un
sub
rat
wh
trig
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Da
Am
red
c
m
llo
h
e®
u
al
er
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cc
eac
r
tr
h
o
u
h
r
id
m
e
is
T
o
a
of
r
E
i
ll was recorded. Thus a percentage of stroke
u
ct
r
T
o
h
n
99
I
5%
o
0±
ey
78 Physical Therap
Physical Therapy in
tched with the synchronization pulse, then
data were time synchronized by importing
timecode to an Excel data sheet. It was then
ssible to ®nd and record the time that
xima and minima of the data occurred for
h stroke examined.
wing trials
e subject was asked to perform two trials of
rowing strokes at a rate of 28 strokes per
nute. Stroke rate was visible on the display
it on the Concept II ergometer. When the
ject felt they were rowing steadily at this
e, they were asked to notify the investigator
ereby a time synchronization device was
gered.
st
m
ce
d
a
st
to
sh
T
(o
1
2
p
5
b
ctrodes or leads and tests were repeated.
artbeat was a consistent source of noise
ifact on the left side that was impossible to
inate. For this reason, it was decided to
ly use SEMG data obtained from muscles on
right side of the chest in the ®nal analysis.
e synchronization of video and Amlab
tems
small light emitting diode (LED) was
sitioned in the corner of the camera lens. A
e synchronization device, triggered from the
lab keyboard, illuminated the LED, and
ultaneously sent a pulse back to the Amlab
tem.
ater, the video frame at which this LED was
ci
S
T
n
to
d
p
st
v
co
th
v
p
fr
e subject was asked to perform maximal
untary isometric contractions of the SA
apular protraction) and the OEA (trunk
ion with contra-lateral rotation).
he SEMG trace for SA was observed during
abdominal testing, and vice versa. Crosstalk
nal that was less than 5% of maximal signal
s considered negligible (Winter et al. 1994).
nacceptable crosstalk or poor signal
ea
ti
a
T
d
d
v
p
th
o
Sport
ta conversion and processing
ta for each trial were converted from the
lab system to an Excel spreadsheet, and
Tim
des
pa
me
y in Sport (2000) 1, 75±84
ration was found for the peak muscle
ivity, and the minimum RR length of each
oke (stroke percentage method).
he convention used in previous research is
divide strokes into four equal phases as
wn in Figure 2A±D (Rodriguez et al. 1990).
ese phases are similarly described for rowing
e oar) and sculling (two oars) (Pelham et al.
5).
n this project, the portion between 0 and
was de®ned as the early drive phase, the
rtion between 25 and 50% was the late drive,
75% was early recovery; and 75% and
ond was de®ned as the late recovery phase.
uced to chunks of information belonging to
h stroke of interest. Each stroke was then
e-normalized and divided into phases to
w comparison between trials and subjects.
e outcome measures obtained for analysis are
ned as follows: SA: the percentage of
ration of each stroke when the peak SEMG
ue for the SA muscle occurred. OEA: the
centage of duration of each stroke at which
peak SEMG value for the OEA muscles
urred. RC: the percentage of duration of
h stroke at which the minimum ribcage
cumference occurred.
oke normalization
ere were two methods used to time-
rmalize the strokes. One allowed the strokes
be described in terms of percentage of stroke
ration and the other divided the stroke into
ases. For both methods, the start of a rowing
oke was de®ned as the frame on the
eotape when movement of the handle
menced in a backward direction (towards
rower's body). This was determined
ually with frame by frame searching.
his start of a stroke was de®ned as the 0%
int in terms of stroke duration, and the video
me and spreadsheet cell preceding the start
the next stroke was de®ned as 100% of the
oke duration.
ach stroke was searched for peak SEMG and
nima of RR values, and the corresponding
ing of events in a stroke could then be
cribed as occurring within one of these
rticular phases of the stroke (stroke phase
thod).
*c 2000 Harcourt Publishers Ltd
*c 2000 Harcourt Pub
M
A
C
Fig. 2 (A) The catch
The mid-drive: Ther
(C) The ®nish: The s
recovery: The hand
B
Reliability of SEMG and RC measurement
The reliability of repeated timing measurements
with the stroke percentage method was
examined between Trials 1 and2. The reliability
estimates obtained for the means of the last ®ve
strokes in each trial, using an ICC model 3
(Shrout & Fleiss 1979) were: SA (ICC ˆ 0.73),
RC (ICC ˆ 0.71) and OEA (ICC ˆ 0.81).
When using the stroke phase method, the
data could not be formally analysed using a
Cohen's Kappa as there was insuf®cient
uniform spread of data across the available
cells. This was due to high levels of agreement
between the trials. There was 100% agreement
for the timing of SA and almost perfect
agreement for the abdominals both within and
between trials. The muscles always peaked in
the same phase. The agreement for the timing
or ribcage compression was less consistent. This
may have been because this event occurred
lishers Ltd
D
or entry: The rower reaches forward by pushing the shoulde
e is no change in body position as the body transmits force
houlders and the arms ®nish off the drive as the upper bod
le is pushed away from the body until the arms are fully ex
uscle action and stress on the ribs in rowing
close to the boundary between phases (near
50%, between late drive and early recovery).
Data analysis
The mean percentages of stroke duration for
peak SA and OEA activity and maximum
ribcage compression were obtained and
compared to determine the sequence of events.
The representative trial used to obtain these
means of timing was Trial 1. Differences in
means within Trial 1 were further analysed
with a one-way ANOVA, with post hoc testing
used for signi®cant ®ndings (Scheffe's F-test).
The level of signi®cance was set at 0.01. This
rigorous level was chosen to reduce the chances
of type II errors.
Differences in timing of the three events
across all subject characteristics (training level,
gender, oar category, weight category and
stress fracture status) were analysed with a
Physical Therapy In Sport (2000) 1, 75±84 79
rs ahead with the arms in preparation for blade entry. (B)
between the oar and the foot-stretcher through the legs.
y leans back and the legs are fully extended. (D) The mid-
tended and the rower slides forward on the seat.
two-way one repeated measure (2W1R)
ANOVA, with post hoc testing used for
signi®cant ®ndings (Scheffe's F-test). The level
of signi®cance was again set at 0.01.
Results
Timing of muscle activity and ribcage
compression
The mean percentages of stroke duration for
events in Trial 1 are summarized in Figure 3. A
schematic representation of these events in a
typical trial for one subject is displayed in
Figure 4, which also shows the extent of overlap
of activity of the two muscle groups.
The serratus anterior was most active just
before the catch of the stroke in the late recovery
phase and the abdominals were most active in
the late drive phase. There was compression of
the ribcage just after the peak abdominal
activity near the ®nish of the stroke. With all
subjects combined, these events were found to
occ
P 5
stro
Differences between groups and
categories
The data were further analysed to search for
ny
t
E
80 Physical Therap
Physical Therapy in Sport
30
25
20
15
10
5
0
20 40 60 80 100 120
Timing (% stroke duration)
C
ou
nt
Abdominals
Ribcage compression
Serratus anterior
Fig. 3 Frequency histogram showing sequence of peak
SA and OEA activity and RC time expressed as a
percentage of stroke duration.
7
6
5
4
3
2
1
0
RCT
S
E
M
G
 a
nd
 R
ub
be
ry
 r
ul
er
 v
al
ue
s 
(m
V
)
OEA OEA
SA
OEA
R
me
Fig. 4 Timing results f
ur at signi®cantly (F[2,102] ˆ 4869.6,
0.0001) different times in the rowing
ke.
a
ca
S
SA
OEA
SA
OEA
SA
Serratus Anterior Abdominals
SA = Serratus Anterior Peak
OEA = Abdominals Peak
RCT = Ribcage Compression Ti
y in Sport (2000) 1, 75±84
RCT RCT
1 2
Rowing Strokes
or a representative rowing trial.
differences in timing between groups and
egories. Means and S.D.s for timing of peak
MG and ribcage compression across subject
SA
ubbery Ruler
*c 2000 Harcourt Publishers Ltd
RCT RCT
3 4 5
*c 2000 Harcourt Pub
M
im
1
a
ro
All Groups 95.80 2.63 40.65
Elite 96.02 2.69 40.22
Club 94.20 1.87 40.30
School 97.17 2.45 41.72
Male 96.45 2.79 41.50
Female 94.91 2.15 39.49
Sweep 96.03 2.61 41.06
Scull 95.29 2.68 39.72
Heavyweight 95.83 2.56 40.83
Lightweight 95.68 3.06 39.90
Stress fracture 95.68 2.86 39.79
No fracture 95.86 2.56 41.07
Table 2 Table of means and S.D.s of peak SEMG and RC t
stress fracture and non rib stress fracture groups for Trial
Peak serratus anterior time
(% stroke)
Peak
(% st
Mean S.D. Mean
groups and categories are presented in Table 2.
ANOVA results for the differences in timing
between groups and categories are summarised
in Table 3.
There were no signi®cant differences in
timing between these groups and rowing
categories ie between training levels, men and
women, weight or oar categories and rib stress
fracture vs non-stress fracture subjects (Table 3).
Discussion
Timing of muscle activity
The results of this study revealed a consistent
pattern of activity of the SA and OEA muscles
whereby the SA peaked just before the catch of
the stroke and the OEA peaked near the ®nish.
This con¯icts with the notion that these chest
wall muscles act together to stress the ribs. The
two muscle groups were clearly working
lishers Ltd
Table 3 Table of ANOVA results for differences in timing b
Group/category
Main group or category effect Main t
F df P F
Training group 1.72 2, 49 0.190 4998.4
Gender 4.35 1, 50 0.042 4916.3
Weight 0.91 1, 50 0.345 4791.0
Oar 0.65 1, 50 0.422 4877.8
Stress fracture 0.38 1, 50 0.538 4847.3
uscle action and stress on the ribs in rowing
es across training groups, oar and weight categories, rib
bdominals time
ke)
Ribcage compression time
(% stroke)
S.D. Mean S.D.
4.00 46.24 3.08
4.46 46.90 3.67
3.27 45.89 2.53
3.97 45.55 2.45
4.58 46.23 3.54
2.73 46.26 2.39
4.02 46.07 2.44
3.91 46.64 4.25
3.96 46.43 2.56
4.27 45.45 4.81
4.03 46.45 3.80
3.97 46.14 2.72
maximally at different parts of the stroke cycle.
Their periods of peak activity did not coincide,
in fact they were widely spaced in the stroke
cycle.
The SA was found to be most active just
before the catch of the stroke as the rower
extended both arms forward. This is in
agreement with the ®ndings of Hosea et al.
(1989), who stated that the SA activates
maximally at the catch of the rowing stroke.
The OEA muscles were found to be most
active just prior to the ®nish of the stroke. This
is an expected ®nding, as the abdominals
would be working eccentrically against gravity
to support the trunk in this position. Rodriguez
et al. (1990) also found the abdominals to be
maximally active at the ®nish of the stroke in
their SEMG studies of the trunk muscles in
rowing. The positions for peak muscle activity
in Figure 4 should be compared with the stroke
phase positions shown in Figure 2(A±D).
Physical Therapy In Sport (2000) 1, 75±84 81
etween groups and categories
iming effect Interaction effect
df P F df P
2, 98 5.001 1.67 4, 98 0.162
2, 100 5.001 1.49 2, 100 0.230
2, 100 5.001 0.18 2, 100 0.838
2, 100 5.001 1.09 2, 100 0.341
2, 100 5.001 0.77 2, 100 0.468
A
the
lev
Th
pea
sim
do
Tim
Th
of
rib
the
rib
wi
the
act
sup
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pre
Jac
199
pro
cau
T
to
rat
ele
acc
pea
Ele
bet
for
the
Ac
mo
dif
rib
cycle, or 120 ms. This means that the peak
act
res
sup
(19
cou
tha
M
wa
is p
in
wa
wh
i
r
f
a
m
q
u
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i
h
e
m
o
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et
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greater bending stresses to the ribs and may
e
cc
Th
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e
s
e
si
o
m
82 Physical Therap
Physical Therapy in
ivity of the OEA muscles may have been
ponsible forthe ribcage compression. This
ports the suggestion made by Karlson
98), that the fractures mimic those caused by
ghing, and are caused by abdominal rather
n SA activity.
easuring change in ribcage circumference
s an indirect measure of skeletal stress, and it
st
v
m
re
th
u
v
co
key ®nding of the current study was that
two muscle groups had peak activation
els in different phases of the rowing stroke.
ere was little overlap in the timing of their
ks of activity so that the notion that they act
ultaneously and maximally to stress the rib
es not seem plausible.
ing of ribcage compression
ere was a consistent and cyclical deformation
the ribcage with each rowing stroke. The
cage was compressed just after the ®nish of
stroke following peak OEA activity. This
cage compression did not correspond in time
th peak activity of SA. Hence the notion that
ribcage is compressed during the rowing
ion by a peak in activity of SA is not
ported by the ®ndings of this study. These
dings are in contrast with statements by
vious authors (McKenzie 1989; Holden &
kson 1985; Boland & Hosea 1994; Gaffney
7) that the SA activity is responsible for
ducing a bending stress to the ribs that
ses rib stress fractures in rowing.
he results indicate that the timing of stress
the ribs closely followed peak OEA activity
her than peak SA activity. It is possible that
ctromechanical and/or acceleration delay
ounted for the difference in timing between
k OEA activity and ribcage compression.
ctromechanical delay is the time interval
ween muscle activity measured by EMG and
ce produced by that muscle activity and is in
vicinity of 50±80 ms (Vos et al. 1990).
celeration delay is the lag between force and
vement produced by that force. The
ference between peak SEMG of the OEA and
cage compression was about 6% of the stroke
tw
w
ci
o
th
co
re
p
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to
D
T
th
co
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im
o
ex
g
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ossible that the ribcage was being deformed
a way that the RR was unable to measure. It
s only able to measure circumference change,
ile the ribs may have been individually
I
rol
inc
Fu
y in Sport (2000) 1, 75±84
n progress to bone micro-damage
umulation and symptomatic stress fracture.
is cannot be ascertained from the current
dy due to problems associated with the
idity of comparing the amplitude of SEMG
asurements between subjects. Future
earch in this area would need to incorporate
concepts of normalization of EMG data
ng, for example, percentage of maximal
luntary contraction (MVC) to be able to
pare across subjects.
isted or deformed along different axes
thout causing a maximal change in ribcage
cumference. It is still possible that the activity
SA imposes a bending stress to the ribs but
t it is not associated with maximal
pression. Further investigation would be
uired to ascertain whether the direction of
ll on the ribs of SA is more likely than that of
A to cause enough bending stress to the ribs
cause a stress fracture.
fferences between subjects in timing
ere were no signi®cant differences found in
timing of chest muscle activity or ribcage
pression between training levels, men and
men, and oar or weight categories. This
plies that rowers establish this motor pattern
the rowing ergometer early in their
erience, which is consistent regardless of
der, category or level of training.
here was also no difference in timing
ween those rowers with and without a
tory of rib stress fractures, or between those
ers who went on to develop stress fractures
pared with those who did not. Since timing
s measured at some interval following or
ceding the stress fractures, it is possible that
berrations in motor patterns exist that lead to
injury, that these are transient and therefore
re not detected in this study.
onversely, it may be the case that
gnitude or volume of muscle activity is more
portant for the development of rib stress
ctures than timing. A greater magnitude or
lume of activity of these muscles could lead
f magnitude of muscle activity does play a
e, stronger OEA muscles may in fact act to
rease the risk of rib stress fracture.
rthermore, the number of loading cycles may
*c 2000 Harcourt Publishers Ltd
abdominal activity and stress on the ribs in
somewhere between the two methods. This is
mobilisation of the thoracic spine, particularly
of the costo-vertebral joints (Wajswelner 1991
stressed by simultaneous peak activity of these
*c 2000 Harcourt Pub
M
an area for further investigation.
Clinical implications
The results of this study revealed that rib stress
fractures in rowing may be related more to
rowing.
Reliability of measurement
The lower reliability for SA activity may have
been due to the inherent variability of
measurement using SEMG (Yang & Winter
1983; Turker 1993; Ng 1993). The use of needle
EMG may have enhanced the reliability of
measurement, but it was not used in this
study due to the risk of puncture of the chest
wall.
SA activity may have been affected by
crosstalk from nearby muscles such as the
latissimus dorsi. This crosstalk would also have
been expected to affect the reliability of
measurement of the OEA, but as this was not
the case, there may have been a source of error
unique to the SA measurements.
The SA activity is related to how far the arms
and scapulae are protracted before the catch,
and no attempt was made to limit this. The
ergometer design tends to limit the extent of
backward motion more than forward motion.
The differing reliability scores between the
muscles may re¯ect this design feature. With a
less rigorous scale, more consistent agreement
between trials was achieved, with almost
perfect agreement for test-retest reliability of
timing using the stroke phase method. This
suggests that when the more conventional
method of dividing the rowing stroke is used,
the measurements of timing of events occurring
in the rowing stroke obtained in this project
exhibited acceptable agreement between trials.
It may be the case that the rowing stroke may
need to be divided into 10 or 12 segments,
be a key factor. Future research could focus on
whether there is a link between abdominal
muscle strength, volume and magnitude of
abdominal activity than serratus anterior
activity, and this implies that excessive
abdominal muscle exercise should be avoided
in cases of suspected rib stress fracture. It
lishers Ltd
muscles in rowing, but that bending stress on
the ribs may be related more to the peak
activity of the abdominal muscles than to the
peak activity of serratus anterior.
Acknowledgement
The authors acknowledge the assistance of the
following organisations and individuals in the
conduct of this project: The Physics Department
of The University of Melbourne, The
Physiotherapy School of the University of
Melbourne, Rowing Australia, the Rowing
Department of the Australian Institute of Sport,
the Rowing Department of the Victorian
Institute of Sport, the Australian Sports
Commission, Mr Steve Martin, Mr Barry
Stillman and Mr Gavin Walsh for their technical
expertise and Mr Noel Donaldson, Head Coach
and 1996). How stiffness of the thoracic spine
and these joints affects the mechanical
deformation of the ribs during the rowing
stroke is a subject for further research.
Conclusions
Peak SA activity in rowing did not occur at the
same time as peak ribcage compression in the
rowing stroke, but compression followed peak
OEA activity after the ®nish of the stroke. The
study showed that the ribcage is not maximally
should be one of the last strengthening exercises
to be re-incorporated after recovery from this
injury. It may be the case that having stronger
abdominal muscles or exercising them
excessively predisposes the rower to rib stress
fractures, but this is yet to be determined.At
the same time, strengthening of the serratus
anterior may be bene®cial as a preventative
measure, as many rowers with a history of this
injury exhibit poor scapula control when
examined clinically.
Finally, rowers with rib stress fractures often
report dramatic relief of pain after passive
uscle action and stress on the ribs in rowing
of VIS Rowing, for this support of this research.
This project was conducted in part ful®lment of
a Master of Physiotherapy (Research) at The
University of Melbourne.
Physical Therapy In Sport (2000) 1, 75±84 83
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*c 2000 Harcourt Publishers Ltd
	Muscle action and stress on the ribs in rowing
	Introduction
	Method
	Subjects
	Procedures
	Data analysis
	Results
	Timing of muscle activity and ribcage compression
	Discussion
	Timing of muscle activity
	Timing of ribcage compression
	Differences between subjects in timing
	Reliability of measurement
	Clinical implications
	Conclusions
	Acknowledgement
	References
	Figures
	Figure1
	Figure2
	Figure3
	Figure4
	Tables
	Table1
	Table2
	Table3