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Original Research

Optimal Elastic Cord Assistance for Sprinting in Collegiate Women Soccer Players

Bartolini, J Albert; Brown, Lee E; Coburn, Jared W; Judelson, Daniel A; Spiering, Barry A; Aguirre, Nick W; Carney, Keven R; Harris, Kenten B

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Journal of Strength and Conditioning Research: May 2011 - Volume 25 - Issue 5 - p 1263-1270
doi: 10.1519/JSC.0b013e318215f575
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Sprint running ability is elemental to sporting activities. Attempts to improve sprint running are critical because sprinting is often used as an evaluation of athletic potential. Training to improve sprint running has become increasingly sophisticated while coaches and athletes examine every consideration when developing training programs. These may include training at the appropriate age (7) with proper nutrition (34), ergogenic aids (35), appropriate drills (3,19) and exercises (15), proper recovery (2,20,24) (both inter and intraworkout), sequence (3), and assisted by a coach's skill and intuition (28). Each of these may lead to optimal sprint running performance.

Training methods for improving sprint performance have typically included general speed and strength (3,4,15,32), velocity-specific strength (15), movement specific sprint-associated exercises (3,4,33), and resistance training (32). Stride length can be developed by improving the sprinter's strength and power, which enables the athlete to apply more force against the ground with the pushing leg while running (15). To enhance force development, athletes need to perform training movements that involve rapid acceleration against resistance, and this acceleration should extend throughout the movement with no intention to decelerate at the end of the movement (27). Technique mastery is said to be essential to increasing stride frequency (28). Mastery of sprint running technique has led to decreased flight time and decreased time in the amortization phase of the running stride (28).

Coaches have made many attempts to increase sprint-running performance by increasing stride length and stride frequency (3,4,17,18,30). Other attempts to increase sprint running performance have included some variation of assisted- or resisted-sprint running (6,8,9,11,12,17,30,32). Resisted-sprint training, research indicates, improves the acceleration (drive) phase by shortening strides and increasing ground force application (8,18,26). Assisted sprint training allows the athlete to run faster than they are normally capable of and is commonly referred to as overspeed training (3,4). Overspeed training seems to improve maximal velocity via increasing stride length, stride rate, or muscular activity of the lower extremities (13,21). When examining the effects of hill slope on acute overspeed running (12) via increasing slopes it was found that 5.8° was the optimal slope for recreationally trained athletes. It is still unclear what assistance load is required for improved sprint performance on level ground. Because not all training environments have access to downhill slopes for sprinting, elastic assistance is another way to induce overspeed. However, there is currently little research on the optimal assistance required to increase sprint performance via elastic cord training. Therefore, the purpose of this study was to determine the optimal elastic cord assistance to increase sprint running performance in collegiate women soccer players.


Experimental Approach to the Problem

This study used a randomized repeated-measures design to assess various assistance levels to determine the optimal elastic cord assisting tension for sprinting acceleration and velocity. Independent variables included 4 different assisting loads compared to body weight. Dependent variables included electronically measured 5-, 10-, 15-, and 20-yd split times and overall 20-yd sprint time.


Eighteen collegiate women soccer players (mean age 19.1 ± 1.1 years, height 168.5 ± 5.5 cm, and mass 64.5 ± 6.9 kg) participated during their off-season. The study was approved by the University Institutional Review Board, and all subjects read and signed an informed consent document before data collection.


Participants attended 3 sessions separated by a minimum of 48 hours. Before testing, participants warmed up by jogging 2 laps around the track (800 m) followed by 5 minutes of dynamic warm-up (2 repetitions of 20 m: a-skips, high knees, butt kicks, lunges, cariocas, running backward). Participants then completed 2 submaximal sprints at approximately 75 and 90% of maximal sprinting speed. The first session included two 20-yd (18.29 m) body weight maximal sprints with no assistance (separated by a 5-minute recovery) to determine baseline sprint running time followed by a pretest orientation session, which included sprinting at 10, 20, 30, and 40% of body weight assistance (BWA). On the second and third visits, participants ran 4 sprints (2 trials each) under 2 BWA conditions with the order of conditions randomized. They were given 5 minutes of rest between each trial and between each condition. All sprints were performed during calm weather and wind conditions of <5 miles·h−1 on grass that was cut to a standardized 2.0 in..

The sprint distance was 20 yd with 5-yd increments and measured using a fiberglass tape. Adjustments to BWA were made by pulling a 60′ elastic cord (3/16" Premium Black 3-Strand Nylon, 1,080 breaking strength, #356964, New England Ropes. Fall River, MA, USA) through a Ronstan 40-mm Fiddle Block, Cleat, Becket, All-Purpose #RF41530 (Ronstan, Sandringham, Victoria, Australia). Elastic cord tension was determined using a Crane Scale (Model #ICS-CCS-500, Industrial Commercial Scales, LLC. North Charleston, SC, USA). The elastic modulus of the 20′ elastic cords used was 6.17 N·m2. Times were determined using an electronic timing system (Speedtrap II, Brower, Salt Lake City, UT, USA) This timing system is an infrared laser timing device that is accurate within 0.01 seconds, according to manufacturer specifications. The timing system was triggered at the beginning by breaking a laser sensor (Figure 1) and the final laser sensor was triggered at 20 yd. Five-yard split times (5-, 10-, 15-, and 20-yd) were also recorded with separate electronic laser timers. All sprint starts had staggered foot placement with forward and rear foot placement selected by the participants. They wore cleats during all trials and were encouraged to put forth a maximal effort on each trial.

Figure 1:
Starting position during the body weight assistance trials. Notice the electronic timers on the grass at the start line and the elastic cord attached to the subject's waist creating a pulling force.

Statistical Analyses

Reliability was measured via the interclass correlation coefficient (ICC). Means and SDs were calculated for all trials. A 1 × 5 analysis of variance (ANOVA) (sprint time × condition) analyzed 20-yd times. A 4 × 5 repeated-measures ANOVA (distance × condition) was used to analyze sprint times for every 5-yd split. Significant interactions and main effects were followed up with simple ANOVAs and pairwise comparisons. All statistics were computed using the Statistical Package for Social Sciences (SPSS Version 17.0). An a priori Alpha was set at 0.05.


The ICC values of repeated sprints across BWA conditions were 0% = 0.78, 10% = 0.48, 20% = 0.58, 30% = 0.81, and 40% = 0.83.

There was a significant main effect for condition for 20-yd sprint time. BWA pairwise comparisons revealed that 10% was significantly <0%; 20% was significantly <0 and 10%; and 30 and 40% were significantly <0, 10, and 20% (Figure 2).

Figure 2:
Sprint times for 20-yd run (mean ± SD) across all body weight assistance conditions. aSignificantly (p < 0.05) <0. bSignificantly <0 and 10. cSignificantly <0, 10, and 20.

There was a significant interaction of condition × distance for 5-yd split times. Simple ANOVAs revealed main effects for condition for each split distance. The 0- to 5-yd split pairwise comparisons revealed that BWA 10 and 20% were significantly <0%, and 30 and 40% were significantly <0, 10, and 20% (Figure 3).

Figure 3:
Sprint times for 0- to 5-yd split (mean ± SD) across all body weight assistance conditions. aSignificantly (p < 0.05) <0. bSignificantly <0, 10, and 20.

The 5- to 10-yd split pairwise comparisons revealed that BWA 10% was significantly <0%; BWA 20% was significantly less than BWA 10%, and 30 and 40% were significantly <0, 10, and 20% (Figure 4).

Figure 4:
Sprint times for 5- to 10-yd split (mean ± SD) across all body weight assistance conditions. aSignificantly (p < 0.05) <0. bSignificantly <0 and 10. cSignificantly <0, 10, and 20.

The 10- to 15-yd split pairwise comparisons revealed no significant difference between BWA 0% and BWA 10%; BWA 20% was significantly less than BWA 0 and 10%; and 30 and 40% were significantly <0, 10, and 20% (Figure 5).

Figure 5:
Sprint times for 10- to 15-yd split (mean ± SD) across all body weight assistance conditions. bSignificantly (p < 0.05) <0 and 10. cSignificantly <0, 10, and 20.

The 15- to 20-yd split pairwise comparisons revealed no significant difference between BWA 0% and BWA 10%; BWA 20% was not significantly different from BWA 0%; BWA 20% was significantly <10%; and 30 and 40% were significantly <0, 10, and 20% (Figure 6).

Figure 6:
Sprint times for 15- to 20-yd split (mean ± SD) across all body weight assistance conditions. bSignificantly (p < 0.05) <10 but not different than 0. cSignificantly <0, 10, and 20.


This study examined the effects of various levels of BWA running on sprint times across 20 yd and for every 5-yd split. Our results revealed that sprint times decreased as BWA increased up to 30% and up to 15 yd. This suggests that training at ∼30-40% of BWA might elicit the greatest enhancement of sprint running across all 5-yd segments in collegiate women soccer athletes.

Assisted sprinting speed in our study increased out to 15 yd. This can probably be explained because of elastic cord tension. Because this was an overspeed study using sprint training, the resultant change in sprinting speed is a function of the elastic towing tension. Therefore, the tension of the cords in this study probably lost their tension relative to the subject's body weight by 15 yd, which left subjects to run at normal BW with no assistance.

Sprint running performance is often used as an indicator of athletic potential. The short duration of sprint efforts during team sport competition indicates that acceleration rather than maximal velocity is more reflective of the demands of field sports (1,5,8,25,31,32). Acceleration is defined as the ability to develop maximal sprint speed in as short a time as possible (25) and is important in the ability to evade a defender, get into position to accept a pass and to defend, it is characterized by slower initial segments followed by increases in running speed until maximum speed is reached. In soccer, short sprints account for 1-11% of the distance covered throughout a match (5). Therefore, we felt it was important to measure sprint time across a relatively short distance.

There are differing opinions as to the distance of acceleration but is generally agreed that acceleration occurs over a relatively short distance. According to previous work (23), 20 m, a distance that athletes rarely exceed when sprinting, represents the first acceleration phase of sprinting. Similarly, studies have indicated that the first 15-20 m represented the acceleration phase of sprinting (29) and that there was a high correlation (r = 0.94) between 10- and 20-m sprint times, which indicates these distances measured similar qualities (36). Acceleration has been described as sprint performance over short distances, such as 0-5 or 0-10 yd (10,25). Other studies (8,13) have extended the acceleration phase of sprinting out to 15 yd. All these distances are representative of our current study.

A variety of training methods using resisted-sprint (14,16,18,26,30) and assisted-sprint methods (11,12,17,34) have been used to enhance sprint-running performance. Assisted training enables athletes to run faster than their maximal speed, which is called overspeed training (9,26). Overspeed is thought to increase speed by increasing stride length (16), stride frequency (21), activity of the neuromuscular system (16), reducing ground contact time, and flight time (17).

Previous studies that have used assisted sprinting via automobiles and downhill slopes have demonstrated improvements in sprint times (11,12,17,34). One study examined the effects of hill slope on acute overspeed running (12) by having participants run sprints at baseline (0.0°) and slopes of 3.4°, 4.0°, 4.8°, 5.8°, 6.9°. Their findings indicated that 5.8° was the optimal slope for recreationally trained athletes. They also performed a follow-up study using college athletes using similar slopes (11) and found that 5.8° was also the optimal slope for college athletes. Similarly, our study examined collegiate women soccer players using 5 experimental conditions (0, 10, 20, 30, and 40 BWA) and found significant decreases in sprint times across conditions and distances up to 30% and 15 yd. Therefore, 30% of BWA seems to be the optimal assisting load for the acceleration phase of sprint running.

A study examining 10 male sprinters and 10 decathletes (17) for sprint running performance at 3% grades running both uphill and downhill found that participants ran faster downhill (V = 9.35 m·s−1) and slower uphill (V = 8.35 m·s−1) when compared to level (V = 8.85 m·s−1). Their data also indicated there was no essential difference between mean stride frequencies under the 3 conditions. However, sprinters had longer stride lengths when running downhill and shorter stride lengths when running uphill when compared to running level. Mean contact time was also much shorter when running downhill (0.109 seconds) than when running uphill (0.115 seconds). These findings indicate that assisted (downhill) running increases running speed via increased stride length. A related study (22) investigating differences between maximal and supramaximal sprint running found that as running speed increased stride rate increased. Large vertical force components in the eccentric and concentric phases and a small horizontal force component in the concentric phase are typical of successful force production in sprint running. Their results demonstrate that, at supramaximal running speeds, increases in velocity are achieved by increasing stride rate. Likewise, it can be suggested that increases in running speed in our study may be explained by either increases in stride length or stride rate because of the elastic cord assistance.

It has been hypothesized (6) that towed sprint training might have adaptation effects on the neuromuscular system. These results showed that mean horizontal velocity was significantly greater in a towed sprint condition than in a maximal sprint condition. Stride length in the towed sprint condition was significantly longer. However, stride rate was not significantly different. The authors suggested that longer stride length and poor positioning of the body relative to the center of mass in towed sprint training supports the contention of poor specificity and possibility negative training effects of this form of conditioning. Contrary to previous research this suggests that a towing stimulus created an exaggerated stride and did not increase the stride rate, which they attributed to a braking force when the stride length is too great. Our study did not measure either, but our results were similar in that increasing BWA loads up to 30% decreased sprint time but there was no change at 40%. This may have been because of an exaggerated stride because of the high assistance load, which actually resulted in the foot contact causing braking.

When examining the relationships (21) between ground reaction forces, electromyography, elasticity, and running velocity of sprinters running at speeds from submaximal to supramaximal (via towing), the electromyography activity of the eccentric stride phase at supramaximal velocity correlated significantly with the relative increases in stride rate. Thus, the increases in running speed in our study may have been because of increased neural activation because of the enhanced foot strike eccentric component caused by the assisting load.

In summary, previous work (6,8,11,12,17,18,21,26,30) investigating the effects of either assisted or resisted sprinting has shown enhanced speed after training. It is important to note that the mechanics of sprinting may be altered during this type of training. However, it would seem likely that these altered mechanics are what lead to enhanced speed.

Practical Applications

This study demonstrated improved sprinting performance up to 30% BWA up to distances of 15 yd. The lack of increase in speed beyond 15 yd is likely because of the loss of elasticity of the cords, whereas lack of improvement at 40% of BWA is likely because of an altering of running mechanics resulting in increased braking forces. Caution should be exercised when using overspeed training, like that done in this study, because it may alter sprint mechanics such as increasing stride length, stride rate, or neural activation. However, it appears that training at BWA loads greater than optimal (≥40% BWA) may have no effect or even a deleterious one on sprint time. For those interested in improved acceleration performance using BWA sprinting with elastic cords, 30% appears optimal in decreasing acute sprint times in collegiate women soccer players from 0 to 15 yd.


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acceleration; body weight; overspeed

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