IN-VIVO MEASUREMENT OF HUMAN TIBIAL STRAINS DURING VIGOROUS ACTIVITY

Our understanding of mechanical controls on bone remodeling comes from studies of animals with surgically implanted strain gages, but in viv o strain measurements have been made in a single human only once, That study showed that strains in the human tibia during walking and runni ng are well below the fracture threshold, However, strains have never been monitored in vivo during vigorous activity in people, even though prolonged strenuous activity may be responsible for the occurrence of stress fractures, We hypothesized that strains >3000 microstrain coul d be produced on the human tibial midshaft during vigorous activity, S trains were measured on the tibiae of two subjects via implanted strai n gauges under conditions similar to those experienced by Israeli infa ntry recruits, Principal compressive and shear strains were greatest f or uphill and downhill zigzag running, reaching nearly 2000 microstrai n in some cases, about three times higher than recorded during walking , Strain rates were highest during sprinting and downhill running,reac hing 0.050/sec, These results show that strain is maintained below 200 0 microstrain even under conditions of strenuous activity, Strain rate s are higher than previously recorded in human studies, but well withi n the range reported for running animals.