SHORT EXPLOSIVE SPRINTING CAN BE IMPROVED BY INCREASING STEP LENGTH: THE EFFECTS OF FOUR TRAINING PROTOCOLS

Lockie, R., & Murphy, A. (2009). The effects of sprint, resistance, and plyometrics training on sprint acceleration kinematics and muscular function. A paper presented at the 14th Annual Congress of the European College of Sport Science, Oslo, Norway, June 24-27.

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This study assessed four common sprint-training protocols (free sprinting, weights, plyometrics, resisted sprinting for changes in acceleration kinematics and maximum muscular power and strength. Males (N = 35) were divided into four groups (Free-sprinting = 9, Weights = 8, Plyometrics = 9, and Resisted-sprinting = 9) matched for 10 m sprinting performance. Kinematic analysis included velocity, step length and frequency, and contact and flight time during a 10 m maximal sprint. Vertical (countermovement jump), horizontal (five-bound test), and reactive (drop jump) power and strength (3-repetition maximum squat - 3 RM) were also assessed. Training involved two one-hour sessions a week for six weeks. The sprinting programs commenced with a volume of 195 m rising weekly by 20-30 m. The weight training program progressed from 75% to 90% 1 RM by week 6. The plyometrics program began with 100 ground contacts, and increased by 12-20 contacts per week.

Following training, each group increased 0-5 and 0-10m velocities by ~9-10%. The weights and plyometrics groups increased 5-10 m velocity by ~10%. Each group increased step length in all intervals. The free-sprinting group decreased step frequency in all intervals and 0-5 m flight time, and increased 0-5 and 0-10 m contact time. The free-sprinting group was the only group that improved in the five-bound test. The free-sprinting, plyometrics, and resisted-sprinting groups increased reactive power. All groups increased the 3 RM squat, with the weights group having the highest percentage gain.

The enhanced step length demonstrated by all groups signified specific horizontal power gains, but only the free-sprinting group increased in the horizontal power test. That change contributed to increased contact time, which allowed for greater horizontal force expression leading to lengthened steps. Reduced flight time balanced the contact time change. All protocols that increased reactive power involved ballistic actions indicative of reactive power. For the plyometrics and resisted-sprinting groups, this adaptation permitted contact time maintenance following training. The weight-training groupís improved strength increased the ability to use concentric force to generate speed, primarily through step-length increases. This was vital as this group did not have significant increases in power, which may limit adaptations for extended sprints (>10m). The improved strength may also have permitted contact time maintenance following training.

Implication. This study revealed critical information about the outcomes of specific training protocols on sprint acceleration. With correct administration, all protocols from the current study can improve acceleration, primarily through step-length development. The underlying power and strength adaptations contributing to speed improvement are protocol-specific. Step length may be the major limiting factor for sprint performance in field sport athletes. It is recommended that specific horizontal power be developed to enhance field sport acceleration. The easiest and most effective form of sprint training is free-sprint training, a finding that reinforces the advocacy of specific training for specific activities.

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