It might seem logical that a runner’s gait and efficiency are at greater risk for breakdown during higher-intensity runs than during slower-paced runs. A recent report published in the Journal of Strength and Conditioning Research (2011; 25 [6], 1479–85) suggests otherwise. Originally, the researchers wanted to see whether high-intensity running to exhaustion would compromise running kinematics (joint motion) and shock absorption. They asked 12 competitive male and female distance runners to complete a 5-minute treadmill warm-up, followed by a self-selected 3-minute workload at 0% grade. The participants then ran at a speed that could be maintained for about 12–15 minutes; this was determined based on a typical 45-minute run. At every 2-minute mark, the treadmill elevation was increased 2.5%. Participants were instructed to cease running once they reached exhaustion. Accelerometers were affixed to each runner’s tibial flare and forehead to measure kinematics and shock attenuation.

The average ventilatory threshold among the runners was 90.2% of HRmax; the average time to exhaustion was 17.8 minutes. With regard to various measures such as maximum knee flexion, time to maximum ankle pronation or shock attenuation, no significant difference occurred between prefatigue and postfatigue. This information proved interesting to the researchers, who noted that shorter, intense runs may be a boon for distance runners interested in reducing overuse injury potential.

“The current results do not support the [original] hypothesis that a brief but high-intensity run will induce changes in ankle and knee kinematics, head and shank acceleration, and shock attenuation,” the study authors observed. They theorized that individuals interested in improved ventilatory threshold should consider including short, exhaustive runs into their regimen. Their conclusion: “Implementing interval running will allow for cardiorespiratory adaptations while limiting the effects of neuromuscular fatigue and possibly injury.”