Running is a practical, affordable and efficient way to become physically active.
Running programs for absolute beginners, taking novice runners from one to thirty
minutes of continuous running, are therefore very popular. Although these programs
are effective in increasing cardiorespiratory fitness and endurance, the effect of a
running program for beginners on the musculoskeletal system is less well
established. The mechanical loading during running causes stress and strains on the
bones, tendons, ligaments and muscles of the lower limb. Biological tissues are
responsive to mechanical loading. Therefore, it can be expected that, when following
a running program for beginners, the musculoskeletal structures will adapt to the
increased loading. Bones respond to increased mechanical loading by changes in
structure, leading to hypertrophy of the bone parts that are under compression. In
the long term, this leads to higher bone mass in people who engage regularly in
weight-bearing exercise. Tendons respond to repeated loading by increases in
thickness and stiffness. During running, the bones and tendons of the lower limb and
in particular the tibia and the Achilles tendon, are loaded repeatedly. Therefore, the
aim of this work was to determine the influence of a typical, 12 week running
program for beginners on running kinematics and kinetics, tibial bone geometry and
density, and Achilles tendon stiffness in novice runners. Understanding how loading
during running leads to tissue adaptations contributes to understanding both
training and injury mechanisms. This can eventually lead to the development of
training programs that improve running performance while minimizing injury risk.
To study musculoskeletal adaptations following a 12 week running program for
beginners, we recruited 71 physically inactive subjects to participate in a running
program. Before and after the running program, running kinematics and kinetics
were measured to calculate loading variables and to determine changes in running
kinematics and kinetics after 12 weeks of training. A pQCT-scan of the lower leg was
performed before and after the running program to determine the changes in tibial
bone properties after 12 weeks of running. Achilles tendon stiffness was measured
non-invasively to determine the influence of the running program on Achilles tendon
stiffness.
ADAPTATION OF RUNNING KINEMATICS AND KINETICS
Running kinematics influence the way that forces are distributed over the different
structures in the body. Because of this relationship between running biomechanics
and structure loading, several previous studies have identified biomechanical risk
factors for developing overuse injuries. These risk factors include increased hip and
knee internal rotation and adduction, increased ankle pronation, and higher loading
rate (the slope of the vertical ground reaction force curve during impact). At the
same time, running kinematics and kinetics influence running performance. In
previous studies, several biomechanical factors have been related to better running
economy, such as lower vertical oscillation of the centre of mass, greater leg
stiffness, less leg extension at toe-off, and lower braking forces. Intuitively, there are
clear relationships between running style (kinematics and kinetics) and injury risk
and running economy. Well trained runners are more economical compared to
novice runners. In addition, incidence of overuse injuries is higher in novice runners
compared to well trained runners. We hypothesized therefore that training would
lead to adaptations in running kinematics and kinetics that have previously been
associated with lower injury risk and better running economy.
Overground running kinematics and kinetics were measured in 27 runners before
and after the running program using motion capture and a force platform. Results
showed almost no changes in running kinematics and kinetics after the training
program. The only significant differences were an increase in peak hip external
rotation moment from 0.02 (SD: 0.02) Nm/kg to 0.03 (SD: 0.02) Nm/kg and a
decrease in peak vertical ground reaction force from 23.1 (SD: 1.9 N/kg) to 22.2 (SD:
1.8 N/kg). This indicates that following a 12 week running program for beginners
does not lead to changes in running kinematics or kinetics that have been associated
with better running economy or injury risk.
ADAPTATION OF THE TIBIA
We evaluated the influence of a 12 week running program for beginners on tibial
bone properties. High bone mass is associated with weight-bearing exercise and is
considered a positive adaptation since it protects against bone injuries. However, it
is unclear whether endurance running provides sufficient mechanical loading to
provoke an osteogenic response. We measured bone geometry and density of the
tibia using peripheral quantitative computed tomography (pQCT) in 11 female novice
runners before and after following a 12 week running program. pQCT results
revealed small increases in bone mass and area at the distal tibia. Loading rate during
running was positively related to increase in bone mass at the distal tibia, indicating
that higher frequency loading on the tibia during running is associated with larger
bone adaptations. However, since these high loading rates have been identified in
the past as a risk factor for developing overuse injuries to the tibia, there is a fine
line between tibia loading and overloading.
ADAPTATION OF THE ACHILLES TENDON
Achilles tendon stiffness, or the ability of the Achilles tendon to resist change in
length when pulled on by a given force, usually increases with training and decreases
with inactivity. However, the specific effect of running on Achilles tendon stiffness is
not well known. We measured Achilles tendon stiffness before and after the running
program in 22 novice runners by measuring tendon length change using ultrasound
during a maximal isometric contraction. Results showed no significant increase in
Achilles tendon stiffness after the running program. Therefore, endurance running
may not provide high enough tendon strains to yield increases in tendon stiffness, or
the Achilles tendon takes longer than 12 weeks to adapt to the loads imposed on the
tendon by the running program.
RUNNING KINEMATICS AND FATIGUE
Runners will often get fatigued during a training session. Previous studies have
shown that several kinematic variables that are considered risk factors for the
development of overuse injuries, increase with fatigue. Therefore, we aimed to
determine the influence of fatigue on running kinematics. We hypothesized that
novice runners show larger changes in kinematics during an exhaustive run
compared to well trained, competitive long distance runners, who may cope better
with fatigue during a training session. Therefore, we used a cross-sectional study
design to compare running kinematics during an exhaustive run on a treadmill
between 15 novice runners and 15 well-trained, competitive long-distance runners.
Results showed that there were changes in running kinematics after the exhaustive
run: pelvic anterior tilt and pelvic rotation range of motion increased in both groups.
Novice runners also showed a significant increase in forward trunk lean over the
course of the run. This confirms that untrained runners are more susceptible to
changes in running kinematics with fatigue than trained runners. However, these
differences are, to our knowledge, not related to injury risk, although this needs
further exploration.
CONCLUSION
In conclusion, we can state that although 12 weeks of running improved the distance
participants were able to run, it did not lead to substantial changes in preferred
running speed, running kinematics or running kinetics. Therefore, although there are
differences in running kinematics between well-trained and untrained runners, there
are no indications that novice runners will improve their running technique over the
course of 12 weeks. Also, the lack of changes in running kinematics and kinetics
indicate that the loading per step during running does not change and therefore that
loading during the running program increased proportionally with the number of
steps. Early indications of increase in bone mass of the distal tibia were found in
female participants, which indicates that running can lead to increased bone
strength. Achilles tendon stiffness did not change, indicating that the 12 weeks of
Achilles tendon loading during the running program was not sufficient to yield
adaptations in tendon stiffness. Despite the limited adaptations in bone and tendon
properties, injury incidence amongst our participants was low in comparison to other
training programs, indicating that this program was well balanced in terms of
musculoskeletal loading and adaptation.
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