# Effect of Velocity and Added Resistance on Selected Coordination and Force Parameters in Front Crawl

Christophe Schnitzler, Tim Brazier, Chris Button, Ludovic Seifert, Didier Chollet

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## To cite this version:

Christophe Schnitzler, Tim Brazier, Chris Button, Ludovic Seifert, Didier Chollet. Effect of Velocity and Added Resistance on Selected Coordination and Force Parameters in Front Crawl. Journal of Strength and Conditioning Research, 2011, 25 (10), pp.2681-2690. 10.1519/JSC.0b013e318207ef5e. hal-02364630

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# EFFECT OF VELOCITY AND ADDED RESISTANCE ON SELECTED COORDINATION AND FORCE PARAMETERS IN FRONT CRAWL

CHRISTOPHE SCHNITZLER,¹ TIM BRAZIER,² CHRIS BUTTON,² LUDOVIC SEIFERT,¹ AND DIDIER CHOLLET¹

¹Faculty of Sports Sciences, Rouen University, Rouen, France; and ²School of Physical Education, University of Otago, Dunedin, New Zealand

## ABSTRACT

Schnitzler, C, Brazier, T, Button, C, Seifert, L, and Chollet, D. Effect of velocity and added resistance on selected coordination and force parameters in front crawl. *J Strength Cond Res* 25(10): 2681-2690, 2011-The effect of (a) increasing velocity and (b) added resistance was examined on the stroke (stroke length, stroke rate [SR]), coordination (index of coordination [IdC], propulsive phases), and force (impulse and peaks) parameters of 7 national-level front crawl swimmers (17.14 ± 2.73 years of swimming; 57.67 ± 1.62 seconds in the 100-m freestyle). The additional resistance was provided by a specially designed parachute. Parachute swimming (PA) and free-swimming (F) conditions were compared at 5 velocities per condition. Video footage was used to calculate the stroke and coordination parameters, and sensors allowed the determination of force parameters. The results showed that (a) an increase in velocity (V) led to increases in SR, IdC, propulsive phase duration, and peak propulsive force (*p* < 0.05), but no significant change in force impulse per cycle, whatever the condition (PA or F); and (b) in PA conditions, significant increases in the IdC, propulsive phase duration, and force impulse and a decrease in SR were recorded at high velocities (*p* < 0.05). These results indicated that, in the F condition, swimmers adapted to the change in velocity by modifying stroke and coordination rather than force parameters, whereas the PA condition enhanced the continuity of propulsive action and force development. Added resistance, that is, "parachute training," can be used for specific strength training purposes as long as swimming is performed near maximum velocity.

## KEY WORDS
swimming, force sensors, adaptation, flume

Address correspondence to Christophe Schnitzler, cschnitzler@unistra.fr.
25(10)/2681-2690

*Journal of Strength and Conditioning Research*
© 2011 National Strength and Conditioning Association

## INTRODUCTION

Swimming performance has been strongly correlated with power and upper body strength (13,14,32). Therefore, competitive swimmers often train with the addition of artificial resistance. There are several methods to do so, and tethered swimming with a bungee cord is one of the most widely used (15,33,40). In this case, the swimmer stays in the same place. However, this method has been criticized because it modifies the swimmer's stroke and streamline (39).

Another method used to apply resistance is that based on the use of a parachute. This method differs from tethered swimming in that a constant load is applied throughout the duration of the swim at a horizontal level and the swimmer does not remain stationary. Previous research on parachute-resisted swimming by Llop et al. (19) compared maximal 10- and 45-second freestyle swims, with and without a parachute. During both parachute swim trials, stroke length (SL) and stroke rate (SR) were significantly lower than in non-parachute resisted swimming. The authors suggested that those spatiotemporal modifications might have an influence on both force production and technique, but these conclusions were not supported experimentally. A more in-depth analysis is therefore required.

Several indicators have been proposed to investigate the coordination used to adapt to constraints and the kinetic changes of a movement. Among them are the index of coordination (IdC) (5) and the examination of force applied by the swimmer in the water (2,3,10,22,24,27). The IdC measures the mean lag time that separates the propulsive phases from 1 arm to the other. For a given swim pace, skilled swimmers are able to maximize the time devoted to propulsion within the cycle and thus exhibit higher IdC compared with less experienced swimmers (5). Moreover, the IdC changes with speed (or pace). At slow paces, expert swimmers have a long gliding phase (IdC < 0%), whereas at fast paces, they overlap the propulsive phases (IdC > 0%); in comparison, the interarm coordination of nonexpert swimmers remains in the catch-up mode (IdC < 0%) (5). A higher superposition-based stroke has been suggested as a more efficient manner of swimming because it generates more
constant propulsive forces, especially at high velocities (8). Thus, expert swimmers are able to increase the cycle time devoted to propulsion, but this indicator remains difficult to interpret because other factors such as gender, anthro-pometry (31), and the ability to generate high propulsive impulses during the cycle (25) may interfere. Indeed, although Chollet et al. (5) and Seifert et al. (30) concluded that skilled swimmers were able to maximize the relative time dedicated to propulsion, Counsilman (9) considered that the ability to push a great volume of water in a short period of time (that is to say, developing high propulsive forces) characterized skilled performance. It would thus be interest-ing to complement such temporal indicators of coordination with force parameters.

The distribution of force over time has been investigated to
examine swimmers' skill levels and their adaptation to
velocity changes. Schleihauf (26) first developed a method-
ology to examine the changes in force development
throughout the cycle in front crawl, using video analysis.
His results showed that in skilled performance, swimmers
generally exhibited 2 peak forces during the cycle. Using the
same methodology, the research of Deschodt et al. (10) and
Maglischo (21) showed that long distance swimmers were
likely to exhibit 1 major peak, during the outswEEP (or push
phase), whereas sprinters emphasized 2 sweeping motions
(namely, insweep or pull phase, and outswEEP). Nonetheless,
this bimodal distribution of peak force remains a feature of
skilled swimmers, because of a deceleration of the hand
between the insweep and outswEEP phases. Counsilman (9)
suggested that this was necessary to find relatively slow
moving water that can be accelerated in a new direction.
Monteil et al. (22) did not find any significant correlation
between force peaks and swim velocity. Together with
Sanders (25), they suggested that the integral of force over
time, or the force impulse, would be more adapted to
examine the changes in force in time domain analysis
in relation with propulsion. However, this video-based
approach has been criticized for not providing a valid
measurement of force development. Payton and Bartlett
(23) showed that this method led to an average error because
of digitization of 20 and 27% for drag and lift, respectively.
Moreover, the model used to determine the drag/lift force
ratio is based on the assumption that the flow of water around
the hand is quasisteady, which is not the case in this type of
movement, where the hand changes orientation constantly
(38). Fortunately, Takagi and Wilson (35) proposed a meth-
odology using hand-mounted force sensors to determine the
changes in force within the swim cycle that allows subjects to
swim without altering their stoke, not unlike the Measurement
of Active Drag (MAD) system where they have to push on
fixed paddles (37) or paddles that might modify the propulsive
force applied by the hands (6,34).

The aim of this study was to investigate the effect of pace
and amounts of resistance (as provided by a parachute) on
stroke (SR, SL), coordination (IdC, swim phases), and force

(force impulse, peak propulsive force) parameters. It was
hypothesized that adding a swim parachute would modify
swimmers' technique, requiring them to apply more strength
for each stroke. More specifically, we expected that (a)
increases in velocity would lead to increases in SR, IdC,
propulsive phase, and force impulse and (b) the additional
drag provided by the parachute would lower SR, SL while
enhancing the time dedicated to propulsion, thus increasing
the IdC and increasing force impulse at equivalent pace.

METHODS

**Experimental Approach to the Problem**

To examine the impact of artificially increasing drag, 3
conditions of additional resistance (provided by a parachute)
were compared. For each condition, 5 paces up to each
swimmer's maximal velocity were imposed. The impact of
these 2 dependent variables (condition and pace) was
examined on spatiotemporal coordination and force param-
eters taken as independent variables.

Subjects

A convenience sample of 7 well-trained male swimmers with 17.14 ± 2.73 years of swimming experience and competitive times of 57.67 ± 1.62 seconds for the 100-m freestyle participated in this study. Their best performance in the 100-m front crawl ranged from 53.3 to 58.7 seconds, which corresponded to 945 and 805 points, respectively, in accordance with the international ranking point system (http://www.swimnews.com/ipspoints). Before the experiment, a brief interview with each swimmer verified the absence of injuries and diseases. Written informed consent was obtained from both subjects and their parents before their participation in the study. Both subjects and their parents were informed of all risks, sources of discomfort, and benefits involved in the study. Procedures were in accordance with the Helsinki Declaration of 1975, and the study was approved by the University of Otago Human Ethics Committee.

Procedure

The swim trials took place in a motorized aquatic flume in a temperature- and humidity-controlled laboratory environment. The experiment was conducted between 8 and 11 AM on a week day, and subjects were instructed to rest the day before, and not to change their dietary, hydration or sleep habits before the experiment. They performed a standardized 20-minute warm-up provided by their coach in the flume before the experiment, which also served as a familiarization period. Each swimmer performed 5 20-second swimming trials in each of the 3 conditions: free swimming (F), low resistance (P1), and high resistance (P2). As shown in Figure 1, the resistance was provided by a swimming parachute (Kytec Swim Resistance Chute; Bloomington, MN, USA), which had an opening diameter that could be adjusted. For P1, it was set at 16 cm and at P2 at 32 cm. All swimmers were familiar with the swim parachute because they used it extensively during training, and the conditions
<figure><img src="image_3.png" /><figcaption>Figure 1. Parachute analysis setup in the University of Otago flume.</figcaption></figure>

(F, P1, P2) were randomized. The velocity-pace relationship for the free-swimming condition was determined relative to the maximal velocity achieved during a 25-m freestyle in a swimming pool. A 10-m section in the middle of the pool was used to calculate the maximal velocity, $V_{max}$, in accordance with the methodology of Chollet et al. (5). Then, in the flume, 5 individual-specific velocities relative to $V_{max}$, or paces, were determined: $V_1$ (60%), $V_2$ (70%), $V_3$ (80%),

$V_4$ (90%), and $V_5$ (100% of $V_{max}$). For all trials, the swimmers were instructed to stay within a delimited zone of 3 m to ensure that they kept following the pace. Whatever the condition, the subjects swam 20 seconds at $V_1$, $V_2$, $V_3$; 15 seconds at $V_4$, and 10 seconds at $V_5$. To minimize fatigue effects, a minimum of 4 minutes of rest between paces and a minimum of 1 hour between conditions (F, P1, P2) were imposed. The velocity-pace relationships for F, P1, and P2 were constructed via passive drag-velocity relationships from 10 passive drag trials and using a 6-20 Borg scale (4) at the end of each trial to ensure that the velocities at which the paces were swum were equivalent across conditions.

## Passive Drag Trials

Passive drag trials were held in each condition to obtain drag resistance at various velocities for the F, P1, and P2 conditions. To obtain the data, the swimmers had to maintain a streamlined position for 15 seconds per trial, holding their breath, while holding an inelastic rope connected to a force load cell. As shown in Figure 2, the drag-velocity relationship was modeled for each condition (P0, P1, P2) as a second-order equation, using a regression analysis: Drag = $a \times V^2 + b \times V + c$. The equation was then solved for $Y1 = Y2$, $Y1 = Y3$, and $Y1 = Y4$ for all swim paces to determine the water flow (swim speed in m·s⁻¹) for the corresponding parachute trials.

## Video Analysis of Arm Movements

Three underwater 50-Hz digital video cameras were positioned around the flume from 2 front angles (45° left and right) and a right profile view. The videos were synchronized using Simi motion software through a marker switch activated before each trial. The video perspectives were combined in the Simi software to allow for quantification of the dependent variables, that is, SR, SL, and IdC. Each variable was calculated on the basis of 3 complete representative swim strokes. The SL (in m·stroke⁻¹) was calculated from the mean velocity (V, in m·s⁻¹) and the movement frequency value (SR, expressed in hertz). The equation to calculate SL was thus $SL = (V) \times SR^{-1}$, as in previous studies (5,30).

## Arm Coordination

The arm stroke was divided into 4 distinct phases, similar to those presented in the freestyle study by Chollet et al. (5):

Phase A. Entry and catch of the hand in the water, which corresponds to the time between the entry of the hand into the water and the beginning of its backward movement.

<figure><img src="image_4.png" /><figcaption>Figure 2. Drag-velocity relationship for each parachute condition: The method to find the velocity that corresponded to the swim pace. Example for pace 1 (A) and 4 (B).</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>Figure 3. Perceived exertion (Borg scale) as a function of (A) pace and (B) condition.</figcaption></figure>

Phase B. Pull phase, which corresponds to the time between the beginning of the backward movement of the hand and its entry into the plane vertical to the shoulder.

Phase C. Push phase, which corresponds to the time between the positioning of the hand below the shoulder and its exit from the water. The summation of the pull and push phase's durations was considered to be equivalent to the arm propulsive time ($P_{pr}$).

Phase D. Recovery phase, which corresponds to the time between the exit of the hand from the water and its following entry into the water.

The absolute duration of these stroke phases was measured for each arm over 3 complete stroke cycles per pace with a precision of 0.02 seconds and was expressed as a percentage of the duration of a complete arm stroke.

The mean duration of a complete stroke was the sum of the propulsive and nonpropulsive phases.

The IdC was calculated as the time gap between the propulsion of the 2 arms as a percentage of the duration of the complete arm stroke cycle (5). The IdC was the mean of IdC$_{left}$ and IdC$_{right}$:

$$IdC_{\text{left}} = \left[ \frac{[\text{Time}_{\text{End of phase C for left arm}} - \text{Time}_{\text{Beginning of phase B for right arm}}] \times 100}{\text{Duration}_{\text{Complete cycle}}} \right]$$

<table><caption>TABLE 1. Stroke, coordination, and force parameters as a function of pace.*†</caption><thead><tr><th>Pace</th><th>V (m·s<sup>-1</sup>)</th><th>SR (stroke-cycle<sup>-1</sup>)</th><th>SL (m·cycle<sup>-1</sup>)</th><th>IdC (%)</th><th>A (%)</th><th>B (%)</th></tr></thead><tbody><tr><td>V<sub>1</sub> (60%)</td><td>0.97 ± 0.2‡S¶</td><td>34.8 ± 3.1‡S¶</td><td>1.68 ± 0.3</td><td>-3.5 ± 6.1¶</td><td>32.7 ± 6.9¶</td><td>22.7 ± 4.2¶</td></tr><tr><td>V<sub>2</sub> (70%)</td><td>1.11 ± 0.2S¶#</td><td>37.7 ± 2.7S¶#</td><td>1.76 ± 0.3</td><td>-3.3 ± 6.2¶</td><td>31.8 ± 7.1¶</td><td>22.7 ± 3.4¶</td></tr><tr><td>V<sub>3</sub> (80%)</td><td>1.23 ± 0.2‡¶¶</td><td>42.4 ± 2.9‡¶¶</td><td>1.74 ± 0.3</td><td>-1.4 ± 5.6</td><td>29.6 ± 6.6</td><td>24.3 ± 3.2</td></tr><tr><td>V<sub>4</sub> (90%)</td><td>1.37 ± 0.3‡S¶#</td><td>46.9 ± 3.4‡S¶#</td><td>1.75 ± 0.3</td><td>0.1 ± 5.2</td><td>27.9 ± 5.6</td><td>25.5 ± 3.2</td></tr><tr><td>V<sub>5</sub> (max)</td><td>1.47 ± 0.3‡S¶#</td><td>51.8 ± 5.5‡S¶#</td><td>1.70 ± 0.3</td><td>2.4 ± 5.8‡#</td><td>24.9 ± 6.4‡#</td><td>27.1 ± 4.4‡#</td></tr><tr><td>Difference</td><td></td><td></td><td colspan="4">NS β = 0.2</td></tr><tr><th>Pace</th><th>C (%)</th><th>D (%)</th><th>P<sub>pr</sub> (%)</th><th>Force impulse (N·S)</th><th>Peak pull force (N)</th><th>Peak push force (N)</th></tr><tr><td>V<sub>1</sub> (60%)</td><td>23.8 ± 4.0</td><td>20.7 ± 2.1</td><td>46.6 ± 6.1¶</td><td>39.4 ± 9.6</td><td>55.4 ± 13.4¶</td><td>77.7 ± 17.8</td></tr><tr><td>V<sub>2</sub> (70%)</td><td>23.8 ± 3.4</td><td>21.7 ± 2.3</td><td>46.53 ± 6.1¶</td><td>38.1 ± 6.5</td><td>54.5 ± 7.8¶</td><td>77.9 ± 13.1</td></tr><tr><td>V<sub>3</sub> (80%)</td><td>24.2 ± 3.3</td><td>21.8 ± 2.2</td><td>48.6 ± 5.5</td><td>37.3 ± 7.0</td><td>60.3 ± 10.8</td><td>78.8 ± 12.5</td></tr><tr><td>V<sub>4</sub> (90%)</td><td>24.7 ± 2.9</td><td>21.86 ± 2.1</td><td>50.3 ± 5.3</td><td>36.5 ± 8.4</td><td>64.4 ± 13.9</td><td>79.2 ± 16.1</td></tr><tr><td>V<sub>5</sub> (max)</td><td>25.4 ± 2.4</td><td>22.7 ± 2.2</td><td>52.4 ± 5.7‡#</td><td>37.5 ± 8.5</td><td>68.7 ± 13.6‡#</td><td>82.5 ± 18.6</td></tr><tr><td>Difference</td><td>NS β = 0.7</td><td>NS β = 0.7</td><td></td><td>NS β = 0.2</td><td></td><td>NS β = 0.2</td></tr></tbody></table>

<footnote>*β = power of the sample size; V₁ = 60% of Vmax; V₂ = 70% of Vmax; V₃ = 80% of Vmax; V₄ = 90% of Vmax; and V₅ = 100% of Vmax; NS = not significant; Ppr = propulsive phase duration; IdC = index of coordination; SR = stroke rate; SL = stroke length.</footnote>

<footnote>†Values are given as mean ± SD.</footnote>

<footnote>‡Significant difference with V₂.</footnote>

<footnote>§Significant difference with V₃.</footnote>

<footnote>||Significant difference with V₄.</footnote>

<footnote>¶Significant difference with V₅ (p < 0.05).</footnote>

<footnote>#Significant difference with V₁.</footnote>
<table><caption>TABLE 2. Stroke, coordination, and force parameters as a function of swim condition.*†</caption><thead><tr><th>Swim condition</th><th>V (m·s<sup>-1</sup>)</th><th>SR (stroke-cycle<sup>-1</sup>)</th><th>SL (m·cycle<sup>-1</sup>)</th><th>IdC (%)</th><th>A (%)</th><th>B (%)</th></tr></thead><tbody><tr><td>Free</td><td>1.5 ± 0.3‡§</td><td>44.3 ± 8.2§</td><td>2.1 ± 0.2‡§</td><td>-3.0 ± 5.7§</td><td>30.3 ± 7.2</td><td>23.2 ± 3.1§</td></tr><tr><td>Open</td><td>1.2 ± 0.2§</td><td>42.4 ± 6.0</td><td>1.7 ± 0.1§</td><td>-1.3 ± 5.6</td><td>29.6 ± 6.5</td><td>24.1 ± 4.3</td></tr><tr><td>Half open</td><td>1.0 ± 0.2‡||</td><td>41.2 ± 6.7||</td><td>1.5 ± 0.1‡||</td><td>0.8 ± 6.5||</td><td>28.3 ± 7.2</td><td>26.0 ± 4.1||</td></tr><tr><td>Difference</td><td>*</td><td>*</td><td>*</td><td>*</td><td>NS β = 0.2</td><td>*</td></tr></tbody><thead><tr><th>Swim condition</th><th>C (%)</th><th>D (%)</th><th>P<sub>pr</sub> (%)</th><th>Force impulse (N·S)</th><th>Pull peak force (N)</th><th>Push peak force (N)</th></tr></thead><tbody><tr><td>Free</td><td>23.7 ± 3.9</td><td>22.8 ± 2.3§</td><td>46.9 ± 5.7§</td><td>36.4 ± 8.9§</td><td>62.1 ± 14.3</td><td>77.2 ± 17.8§</td></tr><tr><td>Open</td><td>24.7 ± 2.7</td><td>21.6 ± 2.0</td><td>48.7 ± 5.6</td><td>36.0 ± 6.4§</td><td>56.4 ± 10.6</td><td>75.2 ± 10.2</td></tr><tr><td>Half open</td><td>24.9 ± 3.0</td><td>20.8 ± 2.1||</td><td>50.8 ± 6.4||</td><td>41.0 ± 7.1‡||</td><td>62.1 ± 12.9</td><td>84.8 ± 15.0||</td></tr><tr><td>Difference</td><td>NS β = 0.5</td><td>*</td><td>*</td><td>*</td><td>NS β = 0.5</td><td>*</td></tr></tbody></table>

$$IdC_{\text{right}} = ([\text{Time}_{\text{End of phase C for right arm}} - \text{Time}_{\text{Beginning of phase B for left arm}}] \times 100)/ \text{Duration}_{\text{Complete cycle}}$$

The duration of each phase was measured for each stroke by 2 independent operators with a blind technique, with a precision of 0.02 seconds.

## Determination of Force Parameters

On the swimmers' right hands, 4 pairs of pressure sensors were glued to the surface of a glove on both the palmer and dorsal sides of metacarphalangeals II, III, IV, and V. The load cell can transduce oscillations of frequencies over a range from 0 to 1,000 Hz. Force applied to the load cell resulted in

changes in the electrical resistance of train gauges housed in the load cell. The sensors were connected via a series of wires to a 12-entry amplifier, connected itself to a computer to record the force data, and calibrated in the water. Force was measured in units of 0.001 N (0.1 g). Sensors were paired by metacarpus, for example, the sensor of palmer side of metacarpus II (PMII) was paired with metacarpus II of dorsal side (DMII). Force differential ($P_A$) was calculated so that in the absence of movement, $P_A = PMII - DMII = 0$. This pressure differential was calculated for metacarpus III ($P_B$), metacarpus IV ($P_C$), and metacarpus V ($P_D$). After this initial calibration of pairs of sensors within the water,

<figure><img src="image_6.png" /><figcaption>Figure 4. Mean values for force impulse (A) and peak push force (B) across swim conditions.</figcaption></figure>

<footnote>*p < 0.05; β = power of the sample size; NS = not significant; P<sub>pr</sub> = propulsive phase duration; IdC = index of coordination; SR = stroke rate; SL = stroke length.</footnote>

<footnote>†Values are given as mean ± SD.</footnote>

<footnote>‡Significant difference with open parachute condition.</footnote>

<footnote>§Significant difference with half-open parachute condition.</footnote>

<footnote>||Significant difference with free swim condition.</footnote>
<figure><img src="image_7.png" /><figcaption>Figure 5. Mean values of the index of coordination across swim conditions.</figcaption></figure>

in-motion mean pressure was obtained using the following equation:

$$P_{\text{mean}} = 0.045P_{\text{A}} + 0.186P_{\text{B}} + 0.554P_{\text{C}} + 0.013P_{\text{D}} + 7.558.$$

The obtained value was then multiplied by the hand plane area (m²) to calculate the resultant propulsive force, according to the Takagi and Wilson (35) method. To obtain this hand plane area, each swimmer had their palmer face of the hand scanned, thumb adducted, and fingers fully extended and packed together. Then, this area was calculated using Mesurim 3.3 software (20). For all subjects, the mean hand surface area was $S = 0.0154 \pm 0.0007$ m².

## Statistical Analyses

The data were first verified for normality (a Ryan-Joiner test) and homogeneity of variance (Bartlett test). Subsequently, multiple 3-way ANOVAs (fixed factors: swim paces, parachute condition; repeated factor: subject) were used to analyze the differences in rate of perceived exertion (RPE), V, SL, SR, IdC, and stroke phases (catch, pull, push, recovery, propulsive phases), and force impulse and the peak forces of pull and push, with sphericity corrections used where necessary. The number of values taken into account was $n = 7$ (swimmers) × 5 (paces) × 3 (conditions) = 105 data points. The Tukey post hoc test was used to locate these differences once a main effect was significant.

For all tests, the level of significance was set at $p \le 0.05$.

## RESULTS

An increase of rating on the Borg scale was observed with each increment of swimming pace (Figure 3A) but not across conditions (Figure 3B).

The changes in stroke, coordination, and force parameters across pace are summarized in Tables 1 and 2 across swim conditions.

## Pace Effect

The SR, IdC, B, $P_{pr}$, and peak pull force increased significantly with pace, whereas A decreased significantly ($p < 0.05$).

<figure><img src="image_8.png" /><figcaption>Figure 6. Percentage of difference between condition 3 (half-open parachute) and condition 1 (free swimming) for force impulse ($F_{imp}$), peak force during push phase ($F_{push}$), stroke rate (SR), index of coordination (IdC), and propulsive phase duration ($P_{pr}$).</figcaption></figure>

For each pace, 3 cycles were analyzed per swim trial, which corresponded to the cycles taken to determine stroke (SR, SL) and coordination (IdC, propulsive phase) parameters. The subsequent portion of the trial was conditioned with a second-order Butterworth filter having a 15-Hz lowpass cut-off. The structure of force output was analyzed in 3 ways, using Matlab routines: force impulse (area under the force-time data, obtained by numerical computation) and magnitude of the 2 main peaks per stroke were noted, to account for the magnitude of the force developed. Video footage ensured that the 2 peaks were measured during the pull and push phases.
## Swim Condition

V, SR, SL, D decreased significantly as resistance from the parachute increased, whereas IdC, B, $P_{pr}$ force impulse, and peak push force increased significantly ($p < 0.05$). The Tukey post hoc test showed that the latter parameters differed only between free-swimming (F) and half-closed (P2) parachute condition.

No significant pace × parachute condition effect was recorded for any parameter.

The effect of swim condition across pace is illustrated in Figure 4 for force impulse (Figure 4A) and peak push force (Figure 4B), and in Figure 5 for IdC.

The Tukey post hoc test did not show any significant difference when paces were compared ($p > 0.05$), although force impulse, peak push force, and IdC were significantly higher in half-open condition (Tables 1 and 2).

The individual modifications consecutive to additional drag in the half-open condition (maximum added resistance) are illustrated in Figure 3.

Figure 6 shows that artificially increasing drag with a parachute led to lower SR in all swimmers as compared with swimming free of constraints. Force impulse and peak push force increased in all swimmers except subjects 1 (negative force impulse) and 2 (no change in peak push force). The IdC and $P_{pr}$ increased in all swimmers except in subject 3.

## DISCUSSION

The aim of this study was to examine the effects of levels of resistance provided by a swim parachute on the kinematics and kinetics of front crawl stroke at different paces. As different velocities were compared, one of the first concerns was to find equivalent paces as a function of condition. For that purpose, we determined the drag-velocity relationship for each drag condition using 10 measurements of passive drag. Admittedly, some controversy exists concerning the relationship between active and passive drag. Indeed, active drag has been found to be either lower (17), equivalent (27,37), or twice as high (7,11) as passive drag, depending on the methodology used. To ensure the reliability of our measurements, we thus used another tool, namely, the RPE as measured by the Borg scale (4). We had to ensure that the subjects were able to properly assess their magnitude of effort. Examination of the results showed that the RPE increased significantly as a function of pace increases. This is important, because it indicates that overall, the participants were able to perceive that the intensity of their effort increased as velocity increased (according to Borg [4]). A closer examination of the data showed that this increase was noted for all participants. With the reliability of the perceived exertion rating confirmed, we then examined whether RPE varied across drag condition. No significant effect of drag condition was found, which suggested that the drag-velocity relationship obtained using passive drag measurements provided data that could be compared across paces. Also

interesting was the lack of significance of the pace × condition interaction, which indicated that these changes with pace and condition occurred whatever the swim condition (F, P1, P2). This suggests that the use of the parachute device did not change the swimmers' global adaptation with pace. These results allowed us to consider the effects of both pace (V1 to V4) and condition (F, P1, P2) on kinematic and kinetic parameters.

For the pace effect, 2 interesting features can be observed in Table 1.

First, from a kinematic point of view, the spatiotemporal and coordination parameters followed the results generally reported in the literature: when swim pace goes from low to high speed, there is a significant increase in SR and IdC, with the latter result being explained by a decrease in catch phase (A) and an increase in pull phase (B) duration (5,28,29). And these modifications occurred whatever the condition of additional resistance, suggesting that the parachute did not seriously disturb the swimmers' adaptation to different velocities.

Second, from a kinetic point of view, the effect of swim pace on the forces developed in the water was examined. This result was of particular interest to us, for no study has yet examined the pace effect on propulsive force, to our knowledge. We chose to examine the changes in peak force and force impulse. Several authors (9,27,36) agree that the 2 main peaks that occur during the stroke, generally during insweep, or the pull phase, and upsweep, or the push phase, are interesting indicators to estimate the magnitude of the force being developed. Moreover, in skilled performance, the magnitude of the gross force developed at these moments in the cycle is close to its efficient component magnitude (36). Our results showed that the peak propulsive force increased with velocity, especially during the pull phase. On the other hand, the overall force impulse did not change significantly across pace. Rouard et al. (24) studied the electromyography of front crawl swimmers in a similar protocol and showed that an increase in velocity did not lead to an increase in the activity of selected muscle of arm, forearm and hands. In accordance with Zamparo et al. (41), who showed that the human body becomes more streamlined when increasing speed, Rouard et al. (24) attributed the change in velocity to the decrease in the frontal body drag resulting from the greater activity of the legs. Our results thus confirmed that increasing velocity does not lead to the development of higher forces. It should be noted, however, that a low power function (β), ranging from 0.2 to 0.7, indicated that the absence of a significant effect on these parameters might have been the consequence of our small sample size. Nevertheless, it is obvious from our results that kinematic parameters (SR, IdC, $P_{pr}$) are of more importance than kinetic ones (force impulse) for adapting to the change in swim pace in experienced swimmers, even though an increase in pull peak propulsive force was observed. In the absence of 3D measurement, it was impossible to get the resultant component of the
force being developed, and thus, these conclusions only concern the gross values of total propulsive force. Nevertheless, these results suggest that swimming at maximal velocity, although very useful for other purposes, might not be a means to develop strength specific to swimming.

The swim condition also showed interesting features. The second issue we examined in this study was the effect of additional resistance provided by a parachute on the kinematic and kinetic parameters of the stroke. Coaches often use additional resistive devices, therefore voluntarily altering the stroke, to put the emphasis on certain aspects of performance. The ability to develop high propulsive forces (13,14,32) and to superpose propulsive actions (thus having an $IdC > 0$, [5,30]) during the stroke characterizes skilled performance in freestyle swimming, especially at sprint paces. Our initial findings showed that swim bouts at fast speeds did not allow greater development of overall force, for force impulse did not increase significantly. A device that allows the swimmer to develop more propulsive force while increasing the superposition of arm coordination would thus be of interest from a training point of view. But using material that alters the stroke does not necessarily lead to such changes. For example, Gourgoulis et al. (12) recently examined the effect of swim paddles on the swim stroke and showed that their use did not significantly change the $IdC$, although the duration of the propulsive phases increased. The results from this study showed that both kinematic and kinetic modifications result from the levels of resistance imposed with the parachute. Indeed, parachute use resulted in significant decreases in $V$, SR, SL. The modifications in $V$ and SL were just mechanical consequences of the protocol, as keeping drag constant in different conditions implies a reduced speed of the flow, and therefore SL. A decrease in SR when resistance is artificially increased was also observed by others (12,18,19), but these studies did not provide detailed data about the potential changes in the stroke coordination. Measurement of $IdC$ and stroke phase duration was provided in this study to further our understanding of the modifications generated by parachute use. Our results showed that the parachute led to a decrease in the catch phase (A), whereas $IdC$ and push phase duration (C) increased significantly. This implies that the use of this device modified the stroke organization by compelling the swimmers to lower their SR and enhance the propulsive phase duration by decreasing the catch phase (A) and increasing the push phase (C) duration. In the P2 condition, the additional resistance forced the swimmers to adopt superposition coordination, which usually characterizes only the best performers (5,29,31). This suggests that training with a device that artificially increases drag, such as a swim parachute, could be an interesting means to work at coordination in superposition mode.

Another interesting finding was that these kinematic changes were accompanied by kinetic changes that did not occur in the free-swimming condition, as shown by

a significant increase in the force impulse (and the peak push force). This indicates that both the mean and peak forces improved with additional resistance from the parachute. This result is important, because it shows that through training with the parachute swimmers can enhance the impulse applied per stroke, which is a crucial element in improving swimming performance (1,16). Interesting data are displayed in Figures 4 and 5, which suggest that in the P2 condition (half open, where additional drag is maximal), force impulse, peak push force, and $IdC$ tended to be higher whatever the pace. However, the post hoc test could not confirm this when the comparison was made pace by pace. This lack of significant effect might be the consequence of the low number of data points compared at each pace ($n=7$), bearing in mind that when paces were considered as a whole, a significant effect was found for these 3 parameters (Table 2). But as the sample of swimmers tested was fairly small, we wanted to have an illustration of individual adaptations to the P2 condition. And indeed, Figure 6 shows that the swimmers' adaptation to the additional drag provided by the parachute was very individual. Although all swimmers lowered their SR and showed a tendency to increase the force, the time dedicated to propulsion and the $IdC$, the magnitude of these variations differed greatly among swimmers. Nevertheless, Figure 6 confirms that parachute use to artificially increase drag modified the technique in such a way that force, propulsive phase and coordination increased, thus confirming the finding presented in Table 2 on an individual basis. This indicates that a change in the stroke mechanics causes the swimming technique to be very different from normal free swimming.

## PRACTICAL APPLICATIONS

This study indicates that the use of a swim parachute may be beneficial for training purposes when swimming near maximal velocity and with high resistance. In this case, kinematic and kinetic modifications in the movement are observed: The duration of the propulsion and the $IdC$ are enhanced. This suggests that using a parachute can help subelite swimmers to adopt the superposition model, which is usually only exhibited by expert swimmers (6,30,31). From a kinetic point of view, parachute use increased the amount of force developed throughout the cycle (both average and peak force). To summarize, the additional resistance provided by a parachute provokes a reorganization in the swimming pattern that would not be typical in normal swimming training, enhancing both coordination and force development. But the observation that these changes occurred only near maximal speed suggests that the application of this type of training device should be limited to high-intensity swimming.

However, these results should be carefully considered. First, this study did not focus on the other effects of high added-resistance training. Although we showed some interesting effects of parachute training on kinematic and kinetic parameters, the actual effect of this type of training on
maximal velocity was beyond the scope of this study. It is
possible that overuse of this method, and thus narrowing the
focus on propulsion enhancement, would have a detrimental
effect on swimmers' active drag. Indeed, we did not directly
evaluate the effect of parachute training on active drag. It is
possible that a less streamline swimming position results from
parachute use, increasing the active drag and thus lowering
swim efficiency. But used in conjunction with other methods,
parachute training might be useful in helping to enhance both
coordination and force development during the stroke.

ACKNOWLEDGMENTS

We would like to thank Triathlon New Zealand, the Prime
Minister's High Performance Coach Scholarship Programme,
Otago Swimming, the New Zealand Academy of Sport, South
Island, which granted the study, and the University of Otago
for their support in the undertaking of this research project.
We also express our great gratitude to Prof. H. Takagi for
having provided us with the material.

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