Brief, intense running doesn't alter kinematics and shock absorption

In competitive runners, a brief, high-intensity run doesn't cause the same kinds of fatigue-related changes in running kinematics and shock absorption as longer training runs, reports a recent issue of The Journal of Strength and Conditioning Research, official research journal of the National Strength and Conditioning Association. The journal is published by Lippincott Williams & Wilkins, a part of Wolters Kluwer Health.

Brief, intense runs might be a useful training approach to help runners reach peak aerobic function while reducing the risk of overuse injuries, the new results suggest. "Implementing interval running will allow for cardiorespiratory adaptations while limiting the effects of neuromuscular fatigue and possibly injury," write John P. Abt, Ph.D., ATC, and colleagues of University of Pittsburgh.

Brief, Intense Running Doesn't Alter Kinematics and Shock Absorption
Responses to brief, high-intensity treadmill runs were studied in twelve competitive male and female distance runners. Run intensity was individualized to each runner, based on his or her aerobic fitness level. The athletes ran at an intense pace—around 95 percent of maximum heart rate—until exhaustion.

The researchers evaluated changes in joint motion (kinematics) and shock absorption during the run. Previous studies have suggested that fatigue leading to altered joint motion and impact is an important contributor to overuse injuries (such as stress fractures) in distance runners.

As intended, the high-intensity runs didn't last long—average time to exhaustion was about 18 minutes. However, the fatigue associated with these brief runs didn't lead to any changes in the kinematic and shock-absorption variables studied.

That result came as something of a surprise, because previous studies have shown changes in joint kinematics and shock absorption in distance runners as they begin to get fatigued. The conflicting results likely reflect differences in the types of training runs studied—running on a treadmill, the runners may not modify their gait pattern in the same way they would during a typical outdoor run. "It is likely that the fatigue experienced during this study that caused the subjects to terminate testing was not the same type of fatigue experienced in a prolonged, lower-intensity running," Dr. Abt and colleagues write.

The study raises the intriguing possibility that brief, high-intensity training runs might provide many of the benefits of training with a lower risk of overuse injuries. "Overuse injuries and changes in running mechanics may be impacted by volume of training—distance and time—more so than intensity of exercise," according to the researchers.

They suggest that runners and coaches could design interval training programs to provide high-intensity training while controlling distance to reduce the risk of injury. However, more research will be needed, focusing on how and when kinematics and shock absorption change during brief, high-intensity runs.