Older Runners Retain Youthful Running Economy despite Biomechanical Differences

Abstract

Purpose: Sixty-five years of age typically marks the onset of impaired walking economy. However, running economy has not been assessed beyond the age of 65 yr. Furthermore, a critical determinant of running economy is the spring-like storage and return of elastic energy from the leg during stance, which is related to leg stiffness. Therefore, we investigated whether runners older than 65 yr retain youthful running economy and/or leg stiffness across running speeds.

Methods: Fifteen young and 15 older runners ran on a force-instrumented treadmill at 2.01, 2.46, and 2.91 m·s(-1). We measured their rates of metabolic energy consumption (i.e., metabolic power), ground reaction forces, and stride kinematics.

Results: There were only small differences in running economy between young and older runners across the range of speeds. Statistically, the older runners consumed 2% to 9% less metabolic energy than the young runners across speeds (P = 0.012). Also, the leg stiffness of older runners was 10% to 20% lower than that of young runners across the range of speeds (P = 0.002), and in contrast to the younger runners, the leg stiffness of older runners decreased with speed (P < 0.001).

Conclusions: Runners beyond 65 yr of age maintain youthful running economy despite biomechanical differences. It may be that vigorous exercise, such as running, prevents the age related deterioration of muscular efficiency and, therefore, may make everyday activities easier.

Figure 1

Metabolic power (W·kg⁻¹) plotted as a function of running speed (m·s⁻¹) for young (open symbol) and older runners (closed symbol) individually. The dashed and solid lines represents the regression for young and older runners respectively. Young and older runners were tested at identical speeds, but for clarity the data are depicted slightly offset from the actual running speeds. The equation of the young runner regression line: metabolic power = 0.85 + 4.15 · speed. The equation of the older runner regression line: metabolic power = 1.33 + 3.65 · speed. The older runners consumed less metabolic power than the young runners across running speeds (p=0.012).

Figure 2

Mean vertical ground reaction force per body weight (BW) for young vs. older runners over time in seconds (s) and across running speeds. Traces are the averages for all young and old subjects. All young and old runners exhibited distinct impact peaks, however the peaks were attenuated by the averaging process.

Figure 3

Leg stiffness (kN·m⁻¹) plotted as a function of running speed (m·s⁻¹) for young (open symbol) and older runners (closed symbol) individually. The dashed and solid lines represents the regression for young and older runners respectively. Young and older runners were tested at identical speeds, but for clarity the data are depicted slightly offset from the actual running speeds. (pound symbol) indicates speed effect. The equation of the young runner regression line: leg stiffness = 13.56 − 0.44 · speed. The equation of the older runner regression line: leg stiffness = 14.10 − 1.27 · speed. Across the range of speeds, older runners had lower k_leg compared to young runners (p=0.002)