Abstract:

Sprint Performance (SP) and the ability to attain maximal sprinting velocity is a major factor in many athletic events. Stride length (SL) and stride frequency (SF) are critical variables when looking at SP. SP can be improved by training overground (on track) (OG), as well as on motorized high-speed treadmills (TM). However, our current understanding is lacking regarding kinematic differences, specifically SL and SF patterns, between motorized treadmill and overground sprinting conditions.
Purpose: 1) To examine the relationship between SL and SF between OG and TM sprinting; and 2) examine if SL and SF are predictors of OG and TM maximal sprint speeds.
Methods: Forty subjects, 20 NCAA sprint athletes and 20 recreationally trained college-aged athletes took part in a single-day testing session. Testing consisted of two 60m OG sprints and two maximal sprints on a highspeed motorized treadmill. In addition to SL and SF, contact time (CT), and flight time (FT) were recorded using a photoelectric cells device. For the OG testing, two timing gates were also used to record maximal sprint speed over the final 10m of each 60m sprint. Subjects were instructed to use the 50-m prior to the testing zone for acceleration in order to achieve maximal speed. For the TM sprinting testing, a motorized treadmill with a max speed of 13.5 m/s was used. Subjects wore a safety harness connected to a steel frame to prevent being ejected from the treadmill. In the testing run, subjects were instructed to gradually transfer their weight on to the moving belt while holding onto the handrails. Subjects were asked to keep up with the belt speed for 3-4 seconds. If successful, belt speed was increased for the subsequent trials until the subjects’ failure to keep up.
Results: Among the 40 subjects, there was a strong positive correlation for speed, CT, and SF performed in OG modality. A correlation was also found between speed, CT and SF performed in the TM condition (Pearson R = 0.94; R = 0.68; and R = 0.65, respectively). In addition, we observed a significant difference (p = 0.00) between OG-speed & TM speed (mean and SD diff = -0.214 ± 0.384), OG-CT & TM-CT (mean and SD diff = -0.010 ± 0.020), and OG-SF & TM-SF (mean and SD diff = -0.471 ± 0.311). No significance difference was observed between OG-FT & TM-FT (mean and SD diff = -0.101 ± 0.248) and OG-SL & TM-SL (mean and SD diff = -65.325 ± 95.750). Among 40 subjects, CT, FT, and SF were found to be predictors of sprint speed in the overground modality (p = 0.000) while SL was not a predictor of sprint speed in this modality. Linear regression for motorized treadmill conditions in 40 subjects showed that CT, FT, SL and SF are all predictors of sprint speed (p < 0.05).
Discussion: Results show that motorized treadmill increases stride frequency dramatically when compared to overground, which could result in the motorized treadmill being used as a training tool to enhance stride frequency. However, the optimal ratio used to achieve sprint speed was altered on the motorized treadmill when compared to overground running. Therefore, while there may benefits to using such an instrument to enhance speed, it is unclear how much improvement is transferred to overground condition. Practical Application: A High-speed motorized treadmill can be used as a supplemental training tool to induce supramaximal sprint running, in aid of acquiring neural muscular adaptations and improvement of stride frequency and ground contact time.