fatigue and tibiofemoral joint biomechanics when transitioning from non-weight
bearing to weight bearing.

Schmitz RJ, Kim H, and
Shultz SJ. J Athl Training. 2015.
50(1): 23-29.

Home Message
: Following a fatiguing exercise protocol, participants
showed increased anterior tibial translation, compressive force, and knee
flexion range of motion during the transition from non-weight-bearing to
weight-bearing. This illustrates an inability of the lower extremity muscles to
stabilize the knee joint.

An athlete is at greater risk for a
noncontact injury, such as an anterior cruciate ligament (ACL) tear, later in
games. While it is believed that fatigue may play a role in ACL injury, little
evidence exists to support this. If this can be verified, clinicians may be
able to identify strategies to better train athletes to stabilize the knee
joint in a fatigued state and limit the risk of sustaining an ACL injury.
Therefore, Schmitz and colleagues completed a cross-sectional study to assess
the impact of a fatiguing exercise protocol on tibiofemoral biomechanics when
transitioning from non-weight-bearing to weight-bearing. The researchers recruited
10 participants (5 male, 5 female, age ~25 years) with no history of knee
injury to the dominant leg. All participants were further screened by a
certified athletic trainer to ensure there was no lower limb dysfunction. All
participants wore motion analysis sensors and were placed into the Vermont Knee
Laxity Device to measure anterior tibial translation when a force of 40% body
weight was applied to the bottom on the foot, which simulated weight bearing. Three
successful trials were obtained before and after a fatiguing exercise protocol.
Fatiguing was accomplished by having the participant perform a repeated leg
press of 60% of their body weight for 15 repetitions with 10 seconds rest until
the participant could no longer complete a full set. Overall, during initial
weight-bearing the authors found a 6% increase in compressive force, a 28%
increase in knee flexion range of motion, and a 22% increase in anterior tibial
translation after the fatiguing exercise compared with before.

The authors present interesting data to
support the concept that knee joint biomechanics are altered in a fatigued
state. Hence, an individual is less able to stabilize his/her knee during
initial weight-bearing when the lower extremity is fatigued. This suggests that
physically active individuals may be at an elevated risk of ACL injury near the
end of activity as the muscles in the lower extremity are less able to stabilize
the joint. Before this is confirmed though more research should be completed in
a larger cohort as well as to take into account participant activity levels to
better understand the effects that training may have on this phenomenon. While
more work may be needed this study may be valuable to clinicians in the future
in terms of activity modification, bracing, and training regiments to further
increase knee joint stability while fatigued. Until this can be completed clinicians
should be observant for faulty mechanics in practice and competitions when
fatigue is likely. Furthermore, clinicians may wish to discuss how to handle
fatigued athlete with their sports medicine team to discuss if the athlete in
question should be removed from activity, and if so who is responsible for
making such a decision.

Questions for Discussion:
Have you seen a correlation between ACL injury and fatigue status of your
athletes? If so, do you intervene when you feel an athlete is fatigued and
exhibiting faulty joint mechanics?

Written by: Kyle Harris
Reviewed by:  Jeffrey Driban

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Schmitz, R., Kim, H., & Shultz, S. (2015). Neuromuscular Fatigue and Tibiofemoral Joint Biomechanics When Transitioning From Non–Weight Bearing to Weight Bearing Journal of Athletic Training, 50 (1), 23-29 DOI: 10.4085/1062-6050-49.3.79