The degree to which standard laboratory gait assessments accurately reflect impact loading in an outdoor running environment is currently unknown.
To compare tibial shock between treadmill and road marathon conditions.
One hundred ninety-two runners (men/women, 105/87; age, 44.9 ± 10.8 yr) completed a treadmill gait assessment while wearing a tibial-mounted inertial measurement unit, several days before completing a marathon race. Participants ran at 90% of their projected race speed and 30 s of tibial shock data were collected. Participants then wore the sensors during the race and tibial shock was averaged over the 12th, 23rd, and 40th kilometers. One-way analysis of covariance and correlation coefficients were used to compare vertical/resultant tibial shock between treadmill and marathon conditions. Analyses were adjusted for differences in running speed between conditions.
A significant main effect of condition was found for mean vertical and resultant tibial shock (P < 0.001). Early in the marathon (12-km point), runners demonstrated higher mean tibial shock adjusted for speed compared with the treadmill data (vertical = +24.3% and resultant = +30.3%). Mean differences decreased across the course of the marathon. Vertical tibial shock at the 40th kilometer of the race was similar to treadmill data, and resultant shock remained higher. Vertical and resultant tibial shock were significantly correlated between treadmill and the 12th kilometer of the race (rs = 0.64–0.65, P < 0.001), with only 40% to 42% of the variance in outdoor tibial shock explained by treadmill measures. Correlations for tibial shock showed minimal changes across stages of the marathon.
These results demonstrate that measures of impact loading in an outdoor running environment are not fully captured on a treadmill.