760 Journal of Strength and Conditioning Research, 2003, 17(4), 760–767  2003 National Strength & Conditioning Association Effects of Resisted Sled Towing on Sprint Kinematics in Field-Sport Athletes ROBERT G. LOCKIE,ARON J. MURPHY, AND CHRISTOPHER D. SPINKS Human Performance Laboratory, University of Technology, Sydney, Kuring-Gai Campus, New South Wales, Australia. ABSTRACT 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. The pur- pose of this study was to explore the effects of sled towing on acceleration sprint kinematics in field-sport athletes. Twenty men completed a series of sprints without resistance and with loads equating to 12.6 and 32.2% of body mass. Stride length was significantly reduced by 10 and 24% for each load, respectively. Stride frequency also decreased, but not to the extent of stride length. In addition, sled towing increased ground contact time, trunk lean, and hip flexion. Upper-body results showed an increase in shoulder range of motion with added resistance. The heavier load generally re- sulted in a greater disruption to normal acceleration kine- matics compared with the lighter load. The lighter load is likely best for use in a training program. Key Words: acceleration performance, resisted sprint training, team sports Reference Data: Lockie, R.G., A.J. Murphy, and C.D. Spinks. Effects of resisted sled towing on sprint kine- matics in field-sport athletes. J. Strength Cond. Res. 17(4):760–767. 2003. Introduction S peed and acceleration are essential components of team sports, such as the various football codes, bas- ketball, and field hockey (9, 16, 20). In addition, max- imum-effort sprints are often too short to allow for the attainment of peak speed for athletes in these sports (33). As a result, the acceleration period of a sprint effort becomes an important focus for any training program for such athletes. Resisted sprint towing has become a popular train- ing method with many sports teams and athletes (28). This can involve an athlete towing a weighted sled, tyre, speed parachute, or some other device over a set distance (13). It has been said that such techniques will increase muscular force output, especially at the hip, knee, and ankle, leading to a potential increase in stride length over time (2, 8, 10, 13, 28). Sled towing is a common resisted sprint training technique and has the added benefits of being relatively unaffected by wind patterns. It has a design that easily allows weights to be secured to the sled for added resistance and consists of the metal sled training device, nylon rope, and harness. The popularity of this training de- vice is reflected in its inclusion in a number of recent publications (6, 14). This form of training is often used with a view to enhancing acceleration performance, even though there is little in the way of scientific evi- dence to support such a practice. In a cross-sectional study, Letzelter et al. (19) ana- lyzed resisted sled towing effects on the kinematics of 16 trained female sprinters using loads of 2.5, 5, and 10 kg. The findings showed that a 2.5-kg load caused a 5.3% decrease in stride length and a 2.4% decrease in stride frequency. At 10 kg, stride length was re- duced by 13.5% and stride frequency dropped by 6.2%. The 10-kg load increased ground contact time by more than 20%, and upper-body lean by approxi- mately 20%. Additionally, an increase of the hip joint angle was found at the start of ground contact. The authors concluded that towing loads produced slower sprint times, changed the dynamics of the stride length/stride frequency relationship, increased sup- port times, and induced changes in upper-body lean and the tendency of ‘‘sitting’’ strides. While this study provided a profile of female sprinters running at top speed, little or no research is available on the effects of resisted sled towing on the acceleration kinematics of field-sport athletes. The purpose of this research was to determine the kinematic variables that are altered as a result of re- sisted sled towing in male field-sport athletes. It is hy- pothesized that sprinting while towing a resisted sled will cause changes in acceleration kinematics. In ad- dition, it is hypothesized that the effect of different loads on kinematics will vary significantly. The results of this study will provide information that will help coaches ascertain the optimal use of this training pro- tocol.