Implied in any linear speed discussion with a Strength and Conditioning Specialist, is the concept of resisted speed training strategies. Some professionals consider resisted speed training as the most efficient sprint training technique on the planet, while other consider it not as effective because of a biomechanical stand point. Different resisted speed strategies include, towing, uphill sprints, sand sprints, and weighted sprints. Tahachnik (1992) explained that towing of weighted devices such as sleds and tires is the most common method of providing towing resistance for the enhancement of sprint performance, although the use of parachutes has also been documented. In fact, resisted towing can involve an athlete towing a weighted sled, tire, speed parachute, or some other device over a set distance (Faccioni 1994).
The function of resisted towing is said to improve the acceleration or drive phase of a sprint. Acceleration is integral to successful performance in the various football codes, including Australian rules, rugby union, and soccer and is potentially decisive in determining the outcome of a game (Spinks et al. 2007). It has been said that resisted towing will increase muscular force output, especially at the hip, knee, and ankle. According to researches improved strength levels allow for the production of greater force and decreased ground contact time, leading to a possible increase in stride frequency. Increased stride length may be achieved by improved utilization of elastic energy during the support stage of the sprint cycle (Spinks et al. 2007).
Regardless of the many benefits of resisted towing speed training, the most effective type of resistant speed training for overall speed and acceleration remains for the most part uncertain.
Weighted sled towing is a common resisted sprint training technique even though relatively little is known about the effects that such practice has on sprint kinematics. Lockie, R.G., A.J. Murphy, and C.D. Spinks (2003) examined twenty men, which completed a series of sprints without resistance and with loads equating to 12.6% (load 1) and 32.2% (load 2) of body mass. Through their findings the participants stride length was significantly reduced by 10% with a 12.6% load and lowered 24% with a 32.2% load. Stride frequency did not change from load 1 to load 2 and only dropped by 6% between the unloaded and loaded trials. In addition, sled towing increased ground contact time, trunk lean, and hip flexion in both loads but, more of an increase happened with load 2. As for the upper body, the results showed an increase in shoulder range of motion with added resistance. The heavier load generally resulted in a greater disruption to normal acceleration kinematics compared with the lighter load. Lockie, R.G., A.J. Murphy, and C.D. Spinks concluded that a lighter load is most likely best for use in a speed training program.
Letzelter et al. (1995) studied the acute effect that different loads had on performance variables with a group of female sprinters during sled towing. The research found that a 2.5-kg load resulted in an 8% decrease in performance over 30 m, and 10 kg resulted in a 22% decrease in sprint performance. Stride length was affected to a greater degree than stride frequency by the increased resistance. As the load increased, the stride length decreased which, accounted for the decrease in velocity speed. Increased loads also caused increased upper-body lean and increased thigh angle at both the beginning and the end of the stance phase. Regrettably, Letzelter et al. did not quantify towing loads relative to body mass or provide anthropometric data on the subjects. It is therefore complicated to relate the results found to earlier recommended loading guidelines.
Spinks C.D., Murphy A.J., Spinks W.L., Lockie R.G. (2007) did a study on effects of resisted sprint training on acceleration performance and kinematics and found that an 8 week resistant speed training group significantly improves acceleration and leg power but, is no more effective than an 8 week non resistant speed training program. Although the study did not find it more effective, how can an athlete increase force production and not increase speed, maybe longer research study should take place.
Both Lockie et al., Letzelter et al. and Spinks et al. studies concluded that the athletes stride length decreased as the load increased. Mutually, both also found that stride frequency did not change much at all with the different loads. Although this is great information neither one of the researchers put any of this to the real test, “Can towing increase speed?" They both gave great information but what coaches want to see are results. A good number of coaches by now should know that your speed is only as good as your technique but, if a greater load can increase arm speed which both researchers agreed, and arm speed accounts for 15-20% speed how can both suggest a lighter load is better for speed training, more research is needed.
Other Types of Resisted Speed Training
Supplementary, to towing there are many other types of resistant training. Some other types of resistant speed training are weighted vest, uphill running, and sand sprinting. A study by Bosco et al. (1986) looked at the effect of increasing body weight (7 to 8%) on sprint athletes over a three-week period, training 3 to 5 sessions per week. The added resistance through weighted vests was worn from morning to evening and the athletes were tested for jumping and running on a treadmill, pre and post experiment. The jump tests included squat jumps, countermovement jump, drop jump and 15 seconds continuous jumps on a resistive platform. The squat jump improved 4.5 cm which helped the hypothesis that the increased loading would have a positive effect upon force production and running speed. Another positive effect of weight vest is that the added mass would increase the vertical force at each ground contact; which would increase the stress placed on the stretch shortening cycle (reactive strength). This would improve the muscle capacity to tolerate greater stretch loads, store more elastic energy, and improve power output, which may increase in stride length. Although Bosco et al (1986). brings up great and valet points about the SSC, how does he know for sure if increasing vertical force in the ground is even beneficial as far as sprinting goes. Remember, your speed is only as good as your technique.
Uphill sprinting had a study conducted by Kunz & Kaufmann (1981) on sprint kinematics maximal sprinting up a 3% incline. They found the velocity to be slower than that of level ground running (8.35m/s to 8.85m/s) and that the subjects sprint kinematics had shorter stride lengths and longer ground contact times. Kunz & Kaufmann believe that uphill sprinting will increase the stress placed on the hip extensor muscle groups as the athlete will attempt to maximize stride length, therefore increasing this component on the flat surface. They feel this training method will develop a shorter ground contact time if the athlete emphasizes fast push off to conquer the effects of the positive grade. An incline of greater than 3% would still be beneficial in developing the forceful hip extensor movements required but will be less specific in the simulation of the specific technical movements of the sprint.
Sand sprinting had little to no research on it. The little research on sand sprinting concluded that it helped increase hamstring strength as well as its flexibility due to the sands unstable surface. Oviatt and Hemba (1991) wrote an article named Sand Blast and in it, stated that “Walking in the sand, however, is almost twice as costly (energy expenditures for physical activity) as walking on firm turf." It follows that sprinting in the sand will compound energy expenditures of a 50% increase. In other words, you can get twice the cardiovascular conditioning in half the time, which, is important because body fat between muscle fibers inhibit rapid contractions of the involved muscle.
Resisted Towing and Kinematics
Steven LeBlanc and Pierre L Gervais (N/A) researched the basic kinematics of sprinting under assisted and resisted conditions as compared to free sprinting in the acceleration and top-speed phases. Free Sprint and assisted sprint kinematics will not be discussed in this section only resisted kinematics compared to sprint start will be discussed because of resisted sprints have more of an impact on acceleration. LeBlanc and Gervais completed 3 trials of resisted sprinting, and a sprint start, using 1 female and 5 male track and field athletes from the University of Alberta. Each sprint was approximately 50m in distance, the participants were also filmed. The linear kinematic measures of interest included average running speed, stride rate, stride length, and ground support time. Angular kinematic measures of interest included average trunk angle, thigh range of motion and peak velocity. The resisted sprinting condition used a parachutechute approximately 1 m2 attached to a waist belt and subjects were given a 30m acceleration zone prior to the filming area to reach top running speed. For the sprint start condition, the blocks were setup 20m prior to the filming area. They established is that there were no significant differences in any of the kinematics being tested and that RS and SS were very similar in average running speed (8.74 m/s vs. 8.76 m/s), stride length (4.03 m vs. 3.92 m), and support time (0.122 s vs. .123 s). This suggests that resisted sprinting has similar kinematics to the acceleration phase of sprinting much more than the velocity phase.
Resistant speed training research on overall effectiveness indicated that all but sand sprinting decreased stride length and had little or no change to stride frequency. Most of the research confirmed that resistant towing is very similar to the acceleration phase of a sprint which is the start. However, there is no well-built indication any of these types of resistant training are better than the other.
From a coaching stand point many professionals today prefer towing because of the trunk position having a forward lean. An athlete cannot have that much of a forward lean with any other resistant speed exercise because of gravity. Sprinting uphill may come a very close second but still one cannot accomplish the lean of that with a weighted sled. Even with the weighted vest the research indicated that the force in the ground hit vertical meaning the athletes ground time was too long. The reason for this may be because the athletes in the research could not handle the weight of the vest and stood up tall to not fall over; keep in mind, many coaches look at a sprint as just a controlled fall. Sand sprinting is also a great resistant speed exercise but, there just is not enough research and data on this type of resistant exercise to put it at the top.
Resistant towing had the majority of the research in all the resistant training modalities but, all had the same conclusions decreased stride length and had little or no change to stride frequency and increased muscular force output, especially at the hip, knee, and ankle. In fact, Mero (1998) found a high correlation between force production in the start and in the velocity phase of the sprint. This indicates a high level of fast force production in top sprinters and reaffirms the importance of strength during the acceleration phase of sprinting which, one can get through resisted speed training.
In the future, there needs to be more research with resistant speed training. For instance, the Spinks (2007) study indicated that there was not significant increase in sprint performance comparing resisted sprint training and non resistant sprint training but, did they take sprint technique or start technique in consideration. As mentioned previous if an athlete can increase ground force through resisted towing as Spinks (2007) mentioned, how can the athlete not become faster with the proper coaching on the technique of sprinting. That is what wrong with the research, there is a lot of research but very little coaching in the research.
Issues in research for resistant speed training should compare different types of resistant training with proper speed technique coaching and see how they compare to overall speed improvement and kinematics. The reason kinematics is still important is because again an athletes speed is only as good as their technique. It is great to know from all this research what is happening biomechanically or muscularly but, the important outcome to all is which will help make you faster in the shortest amount of time. Coaches and athletes want to know the best modalities of resistant speed training and how they compare to each other, more importantly how they compare to overall speed improvement.
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- Faccioni, A., (1993) Resisted and assisted methods for speed development. Part 2. Strength & Conditioning Coach. 1(3), 7-10
- Gervais, P., LeBlanc, J. S. (N/A). Biomechanical analysis of assisted and resisted sprinting. Faculty of Physical Education and Recreation, University of Alberta, Edmonton, Alberta, Canada. 1-4.
- Kunz, H., Kaufmann, D.A. (1981) Biomechanics of hill sprinting. Track Technique. (82), 2603-2605.
- Letzelter, M., Sauerwein, G., and Burger, R. (1995). Resistance runs in speed development. Modern Athlete and Coach. (33), 7Ã¢â‚¬â€œ12.
- Lockie, R.G., A.J. Murphy and C.D. Spinks. (2003). Effects of resisted sled towing on sprint kinematics in field sport athletes. The Journal of Strength and Conditioning Research. 17(4), 760-767.
- Mero, A. (1988). Force-time characteristics and running velocity of male sprinters during the acceleration phase of sprinting. Research Quarterly for Exercise and Sport, 59(2), 94-98.
- Oviatt, R. and Hemba, G. (1991). Oregon State: Sandblasting through the PAC. National Strength & Conditioning Association Journal. 13(4), 40-46.
- Spinks C.D., Murphy A.J., Spinks W.L., Lockie R.G. (2007). The effects of resisted sprint training on acceleration performance and kinematics in soccer, rugby union, and Australian football players. The Journal Of Strength And Conditioning Research. 21 (1), 77-85.
- Tabachnik, B. (1992). The speed chute. National Strength & Conditioning Association Journal. 14(4), 75- 80.