Original Research: Isometric Force-time Characteristics and Test-Retest Reliability of a Rowing Specific Isometric Assessment
Published On: January 29, 2019Categories: Research
reliable means of measuring strength and RFD in key rowing positions may be
valuable for those who wish to assess the impact of strength programs on force
output during rowing. The purpose of this study is to investigate the isometric
force –time profile and reliability of an isometric test involving a rowing
specific body position.
elite female rowers volunteered in the study. Test-retest reliability of the
catch position isometric pull test (ISoRow Pull) was examined using a repeated
reliability of the isometric pulls was calculated using the intraclass
correlation coefficient (ICC) and coefficient of variation (%CV) set at 90%
confidence interval. Standard error of measurement (SEM) was calculated to
determine the minimum detectable change (MDC) for PF, TPF and peak RFD.
The average peak force of the
two sessions was 817.6 ± 127.1N and average TPF was 630±21ms. Intraclass
correlation coefficients, MDC and SEM between the two tests were r=0.98 (90%
CI= 0.95-0.99) MDC=64.1N, SEM= 14.04N for PF and r= 0.67 (90% CI= 0.36-0.85)
MDC 0.3s, SEM= 0.11s for TPF respectively. Coefficient of variation was 1.9%
(90% CI =1.3-2.5%) for PF and 13.9% (90% CI =7.3-20.6%) for TPF. RFD at each
time interval examined was highly reliable with ICC ranging from 0.96-0.99 (90%
CI 0.91-1.00) and an average CV% of 2.51±0.96.
IsoRow Pull is a reliable test of rowing specific strength that provides a
potential tool for future research on the transfer of strength training to
various aspects of rowing performance.
Key words: Rate of force
development, Sport specific, Peak Force, Time to Peak force
training is a valuable part of a rowing program as it has been shown not only
to improve measures of strength with no negative impact on aerobic performance
(17), but stronger rowers are more likely to be selected to a crew for
competition (18). Accurately assessing
strength levels and changes in strength helps guide program development and
provides a quantifiable measure of the success of the strength program.
Strength testing for rowing has frequently involved traditional free weight
exercises like squats, bench pulls, deadlifts, cleans, leg presses, and
vertical jumps (4, 17, 18, 21). While providing valuable information for
adjusting and individualizing strength programs in the weight room, traditional
weightlifting based tests do not necessarily reflect the true strength requirements
of rowing (20).
function tests are most valid and relevant when they reflect changes in sport specific
performance, which is ideally highly quantifiable (23). The concept of movement
pattern specificity in strength training has been generally supported in the
literature, with the greatest improvements in performance occurring when movement
pattern, speed and range of motion trained mimics the sports performance
demands (22). To date only two studies many years ago have looked at strength
levels of rowers using a rowing specific position, but not necessarily
mimicking the rowing movements and /or speeds. Koutedakis and Sharp (16) used
strain gauges and a specifically designed bench to assess the upper body
strength of junior male rowers by having them pull as hard as possible with
arms and trunk while the legs remained straight and braced against a footplate,
a position similar to the final quarter of the drive phase of the rowing
stroke. Secher (25) examined isometric
rowing strength of elite Danish rowers in a position that simulated mid-drive
of the rowing stroke and compared it to isometric strength of individual muscle
groups. Their results further support the importance of specific body positions
when using an isometric test, and of the eight muscle specific isometric
strength tests only hand grip significantly correlated to rowing specific
isometric strength (r= 0.43; P<0.01).
More specifically, Kawamori et al (12) have suggested that joint angle
and body position for an isometric test should be as close as possible to the
actual dynamic movement of interest if a strong relationship between dynamic
and isometric force development are expected to be seen.
The catch is the link between the recovery and drive phases of the rowing stroke. It occurs from the moment the blade of the oar enters the water until the blade is completely covered and locked into the water (24) ( http://www.worldrowing.com/photos-videos/videos/essential-sculling-technique ). The leg drive, initiated from the catch, is an important performance variable for overall technical effectiveness (14). An earlier increase in force and velocity results in a higher average boat speed and longer distance travelled per stroke (15).
a reliable means of measuring strength and rate of force development (RFD) in
key rowing positions such as the catch, may be valuable for both researchers
and practitioners who wish to assess the impact of strength training programs
on force output during the rowing stroke. Therefore, the purpose of this study
is to investigate the isometric force –time profile and determine the
reliability of an isometric test involving a rowing specific body position in
elite female heavyweight rowers.
Experimental Approach to the Problem
reliability of the catch position isometric pull (IsoRow Pull) test was examined
using a repeated measures design. Athletes were asked to perform IsoRow Pull
trials on two occasions seven days apart.
Both tests occurred the middle of the afternoon following a standardized
day off from training. Training in each week prior to the testing was similar,
consisting of ~18.5 hours of total training (~4.5 hours – strength; ~10.5 hours
– water rowing; ~1.5 hours – cross training; ~1.25 hours – ergometer; Remainder
– stretching and rehab).
To negate any potential learning
effects, all subjects recruited had previous experience with apparatus and
protocol during pilot work completed 12 weeks prior to the current study. In addition, three days before testing all subjects
were asked to practice the IsoRow Pull
This re-familiarization with apparatus and procedures was achieved through
performing four submaximal and two maximal pulls from their catch position.
elite female rowers volunteered in the study (height = 182.2±4.7 cm; weight =
81.0±6.1 kg; age= 25.1±2.7 years). All participants were full-time members of the
Rowing Canada national team and completed 18-22 hours of training per week for
at least four months prior to testing. Fourteen of the 16 women had competed at the
2014 World Rowing Championships as such this cohort is defined as elite. All
subjects provided informed consent prior to participation in this study. The
study was approved by the Canadian Sport Institute Ontario Research Ethics
force and RFD were determined using a purpose built isometric rowing apparatus with
hand and foot adjustments that allowed the subject to assume similar trunk, hip
and knee positions as they would on an indoor rowing ergometer (figure 1-
IsoRow). Subjects self-selected the catch position which was then visually verified
by the coach. Settings of the feet and
hands were noted and the same settings were used for the second test. Data was
collected using a
PS2142 Pasco force plate (Pasco Scientific, Roseville, CA) placed on the
footplate of the isometric rack sampling at 500Hz using Pasco Capstone data
acquisition and analysis software. Subjects performed four maximal isometric
contractions separated by 3 minutes. They were instructed to pull as hard and
as fast as possible for 4 seconds for optimal results (Haff et al, 1997). Prior
to the IsoRow Pull test all
subjects completed a standardised warm-up incorporating 10 minutes of dynamic
stretches followed by three progressive isometric pulls that was exactly
mimicked before each of the two testing sessions.
smoothed using a centre weighted Savitzky-Golay
algorithm of the fourth order. The best of four trials, as determined by
the highest peak force, was used in all calculations. Forces normal and parallel to the force plate were
measured and resultant force in the direction of the seat calculated. Force every 50ms
was recorded for the first 500ms of the isometric effort. At race stroke rates the drive phase of the
rowing stroke is a low as 600ms (3). Since this study was designed to look at
the force profile at the catch position, which is a relatively small part of
the drive phase, it was felt that 500ms is adequate to determine a rowing stroke
specific RFD. Predetermined time bands have been shown to be more reliable for
determining RFD (7) so rate of force development was calculated as slope of
force-time Tracing from the first sustained increase of 10N from baseline to the force at the end of each of the time bands (0-50,
0-100, 0-150, 0-200, 0-250, 0-300, 0-350, 0-400, 0-450 and 0-500 millisecond). Baseline was
established as the average force during a 5s ready period immediately prior to
the initiation of the isometric contraction. Time to peak force (TPF) was the
time from the initiation of the contraction, (i.e., the first sustained
increase of 10N above baseline), until peak force was reached. Using the
methods proposed by Zatsiorsky (32) the index of explosive strength (IES), the S-gradient,
a characterization of the rate of force development at the beginning of a
muscular effort, and the A-gradient,
which is used to quantify the rate of force development in late stages of
explosive efforts, were calculated using
the following equations: IES = Fm/Tm where Fm is the maximum force and Tm is
the time to maximum force; S-gradient = F0.5/T0.5 where F 0.5 is 50% of the
maximal force and T0.5 is the time to 50% maximal force; A gradient = F 0.5/ (T
Test–retest reliability of the isometric pulls was calculated using the
intraclass correlation coefficient (ICC) and coefficient of variation (%CV) set
at 90% confidence interval (11). Standard error of measurement (SEM) was calculated to
determine the minimum detectable change (MDC) for PF, TPF and peak RFD. The SEM was calculated by
multiplying the SD
variable by the square root of 1 minus the ICC of the variable (30). The value
of 1.96 x SEM represents the 95%
confidence interval (95% CI) and defines the possible range of the measurements
because of error. A change greater than 1.96 x SEM represents a change that is unlikely to be the
result of error and, therefore, is the MDC (27). The ICC were evaluated using the
following criterion measures; poor ICC< 0.50, moderate 0.50 < ICC <
0.70, good 0.70 < ICC < 0.90, and excellent ICC > 0.90 (2). Acceptable
reliability was determined as a good ICC and a CV < 15% (7). Paired T-tests
were used on each time interval for RFD as well as PF and TPF to determine if
there were any differences between the testing sessions. Significance was set
at P≤ 0.05.
The average combined peak force of
the two sessions was 817.6 ± 127.1N and average combined TPF was 630±21ms of
the four second effort. Intraclass correlation coefficients, MDC and SEM between
the two tests were r=0.98(90% CI= 0.95-0.99; p< 0.0001) MDC=64.1N, SEM=
14.04N for PF and r= 0.67 (90% CI= 0.36-0.85; p= 0.0013) MDC 0.3s, SEM= 0.11s for
TPF respectively. Coefficient of variation was 1.9% (90% CI =1.3-2.5%) for PF
and 13.9% (90% CI =7.3-20.6%) for TPF.
Rate of force development and
reliability measures for each 50ms time period can be found in table 1. Test-retest
scatter plots of early (50-150ms) middle (200-350ms) and late phases (400-500ms)
of the isometric effort can be seen in figures 2-4. The S- gradient had
acceptable reliability but both the IES and the A- gradient had only moderate
ICCs (table 3).
1. Average of Two Trials for Rate of Force Development for each 50ms interval
ICC = intraclass correlation; CI
= confidence interval; SEM= Standard Error of Measurement; MDC= minimum
2. T-Test Results for each 50ms interval
1 RFD (N·S-1)
2 RFD (N·S-1)
Difference (Test 2-Test 1)
3. ICC and CV for IES, S-Gradient and A-Gradient
T-Tests revealed no significant
differences between test sessions for any of the RFD time intervals (p>0.05)
measures (table 2). There were no differences between trials for PF
(812.81±128.59 N, 818.34±121.34 N, p=0.399) but there was a significant
difference between trials for TPF (0.59±0.20s, 0.68±0.21s, p=0.025).
This study examined the
test-retest reliability of the isometric PF and the force profile of elite
female rowers in a position that simulates the catch position of the rowing
stroke (IsoRow Pull Test). Within this
experimental group, the relative reliability measures were excellent for RFD at
each 50ms time period analyzed (ICCs 0.96-0.99). These correlations are in
agreement with those found by Haff et al (7) using predetermined time zone
bands in an isometric mid-thigh pull. Peak RFD (PRFD) occurred in the 0-100ms
interval and had an ICC of 0.99 (90% CI=0.98-1.00). This is higher than the ICC
range of 0.56-0.65 that Young, Haff, Newton and Shepard (31) found for various
elbow angles of the isometric bench press. The authors suggested that their low
ICC values for PRFD may be due to the experience level of the subjects, most of
whom were primarily involved in lower body sports and may not have had as much
experience with a maximal effort bench press. Studies employing subjects who
use a dynamic multi-joint movement similar to the isometric test movement as a
regular part of their training programs seem to produce higher ICC values. Intra-class
correlations for PRFD in weightlifters performing an isometric mid-thigh pull
has been shown to range from r=0.81 to r=0.96 (6, 12), while the ICC for
untrained subjects performing the same test has been shown to be r=0.75 (13). In
the current study all subjects were highly experienced rowers and very familiar
with the body position assessed as it is a key part of the rowing stroke.
Absolute reliability of RFD (%CV)
was below 5% for all time intervals (range= 1.4-4.6%). The absolute reliability
tended to be lower in the first four intervals, up to 200ms, than in the rest
of the test. Motivation and mental preparation have been suggested as factors
in the reliability of RFD (31). It can
be speculated however that while instructed to pull as hard and as fast as
possible, elite endurance athlete’s cohort spend relatively little time performing
maximal explosive movements and therefore, may not initiate the pull as
aggressively as a speed or power athlete.
Peak force was highly reliable
with a %CV = 1.9% (90% CI= 1.3-2.5). Peak force values in the current study are
lower than those reported by Secher (25), the only other study to use a rowing
specific position that incorporated both upper and lower body. In an equivalent
level of male performer they found rowing forces of 204±3.9 kp. Gender
difference in subject pools between the two studies may account for some of the
difference. Male subjects have been shown to produce up to 50% more power and
force on a rowing ergometer (8) and during the start of a race (26) than
similar calibre female rowers and 50% more force in an isokinetic knee extension
at 1.05 rad/sec (9). The current study also used the catch position compared to
a mid -drive position used by Secher (25). Mid-drive which typically coincides
with the highest forces in the rowing stroke (28).
The IsoRow time to peak force of
630 ±21ms was the least reliable of all the measures in this study on both
absolute (ICC = 0.67; 90% CI=0.36-0.85) and relative terms (%CV= 13.9%; 90% CI=
8.0-20%) displaying only moderate reliability. As a result those variables
using Tm in their calculation, the IES and A-gradient, were also not
reliable. Time to peak force values were
slower than the 222±23.51ms reported by Haff et al (5). This is probably due to
the type of subjects in the study pool. The authors used subjects experienced
with weightlifting movements. Power athletes typically produce more force and
have a higher RFD in explosive efforts (10, 29) so it is not surprising that
the rowers in this study produce force less quickly than subjects who regularly
use explosive movements.
In conclusion, the present study
suggests that the MDC in PF and RFD of an IsoRow Pull test would be the most
useful tool for rowing practitioners, giving them a value against which they
can assess changes from their programs to determine how much change has occurred
beyond the expected variation. For a test to be useful to a practitioner it has
to be sensitive enough to pick up the changes that would typically be seen
through training in the group in question. For instance, a test with an MDC of
15% is not very useful if the changes typically seen through training are only
5%. Unfortunately, there is very little data available on the change in fitness
or performance parameters in world class rowers. To the knowledge of this
author only Lawton, Cronin, and McGuigan (18) have published data on strength
changes in world class female rowers. The 9.1 ±8.5% (p=0.01) and 12.3 ±8.6%
(p=0.10) changes in 5 rep leg press and a knee high isometric pull following 14
weeks of training are similar to the MDC values for peak force of 7.8% and peak
RFD of 9.5% for this study, suggesting that the IsoRow Pull test examined in
this study may be sensitive enough to detect strength changes in elite female
testing for rowers has traditionally focused on free weight exercises involving
the key musculature used in rowing but not rowing specific body positions. The
current study has examined the reliability of an isometric test in a key rowing
body position, the catch (IsoRow Pull). While much work still remains to be
done on the relationship between specific isometric force and measures of
dynamic rowing force, a reliable, easy to administer test of rowing specific
strength provides a potential tool for future research on the transfer of
strength training to various aspects of rowing performance and studies on the
relationship between on water and off water force production.
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