Page 108 - Journal of Special Operations Medicine - Spring 2016

Foot strike patterns were assessed by high-speed filming, The only study to prospectively examine the association
and injury data were obtained from a questionnaire. In- between loading rates and running injuries was that of
29
juries were limited to those that required modified train- Nigg, in which data from a previous study were re-
ing for at least 1 week because of pain or discomfort analyzed. These data included 131 runners who had
and that occurred as a result of running. There were their loading rates obtained before the start of the study.
296 rearfoot strikers (87%) and 45 nonrearfoot strikers In the subsequent 6 months, injuries were tracked by
(13%). The proportion of Soldiers reporting any life- a sports medicine physician. Runners were separated
time running injuries was 50% in rearfoot strikers and into three groups, representing low, moderate, and high
56% in nonrearfoot strikers (p = .51). Over the previous loading rates, and injuries were examined in each of
5 years, overuse injury incidence was also similar for these groups. Results are shown in Figure 5 and were
Soldiers with these foot strike patterns (rearfoot strik- not what might be expected: injury rates declined as im-
ers, 32%; nonrearfoot strikers, 31%; p = .89). It is not pact forces increased.
clear how many miles the Soldiers were running, but
estimates from the data provided in the article suggest Figure 5 Association between running injuries and
an average of about 12 miles/week. prospectively obtained loading rates. Approximate p-value
was calculated based on data from Nigg. 29
Thus, it is not clear at this point if the running foot
strike pattern influences injury incidence, although there
is likely benefit for individuals suffering from CECS in
adopting a forefoot strike pattern. The Harvard study
suggests that elite runners who perform longer weekly
distances may benefit from a forefoot strike, but one
problem with this study was that foot strike patterns
were not assessed for the entire length of the investi-
gation; some athletes may have adopted another foot
strike pattern later in the study. The Fort Carson study
suggested that among Soldiers who run limited weekly
distances, there is no difference in injury incidence by
foot strike pattern. One serious limitation of the Fort
Carson study was the self-reporting of injuries over long
time periods (lifetime and 5 years). Studies have shown
that recall of injuries progressively decreases as the re- Despite being somewhat counterintuitive, the finding
call period increases. 21,22 In addition, it should be noted that injury rates declined with higher impacts is consis-
that Soldiers undertake a wide variety of activities, with tent with research on bone strength that suggests high
running usually representing only a small proportion of impacts may reduce the possibility of at least one type of
their regular physical activity. Thus, it is likely that any injury: those involving bone stress. Individuals partici-
influence of running foot-strike pattern on long-term pating in sports involving high impacts (e.g., basketball,
injury rates may have been masked in the Fort Carson volleyball, running) have higher bone mineral density
study by the strong contributions to injury rates by than those in nonimpact sports (e.g., swimming). 30–32 In
33
many other types of Soldiers’ physical activities. a different type of study, Warden and colleagues re-
peatedly mechanically loaded rat bones for short bouts,
3 days per week for 5 weeks, and found that this regular
Injuries and Loading Rates
repetitive loading resulted in a twofold improvement in
A number of studies 23–28 have compared loading rates the structural properties of the bone over that time pe-
between runners who had a prior stress fracture or plan- riod. Most importantly, however, this twofold improve-
tar fasciitis and runners without these injuries. Most ment in the bone structure provided a 100-fold increase
studies 23–25,27,28 matched injured and uninjured subjects in the resistance of the bone tissue to fatigue and dam-
on characteristics like age and running mileage. Some age when it was repeatedly loaded to the same level in
studies found that the runners with the injuries had a a single session until it broke. Thus, high impacts may
greater loading rate on ground contact than did runners improve bone strength and lower the risk for bone stress
without these injuries, 23–25 but other studies did not find injuries, but how high impacts may influence other types
a difference. 26–28 A few of the studies finding positive re- of injuries involved in running is not clear.
sults 23,24 admitted the most serious limitation to studies
of this type: it was not clear if the more-rapid loading Like the data on foot strike patterns, data on associa-
rate was present before the injury, or if it had developed tions between impact forces and running injuries do not
after the injury. present a well-defined picture. It is not clear if loading

92 Journal of Special Operations Medicine Volume 16, Edition 1/Spring 2016