Inhibition (AMI) refers to an impairment caused by an ongoing
reflex inhibition of the musculature surrounding a joint. Joint
injury causes AMI to the surrounding musculature as a protective
mechanism to the injured joint. Unfortunately, AMI may impede
recovery after injury by preventing complete activation of a
muscle. Quadriceps Activation Failure after knee joint reconstruction
may persist for years after major joint trauma and reconstruction.
A related phenomenon called central activation deficits (CAD)
also occurs after total knee arthroplasties (TKA), performed
to alleviate knee osteoarthritis (OA)-related pain and disability.
Hamstrings dysfunction also is present and should be addressed.
The exact mechanisms causing and regulating quadriceps and
hamstrings AMI after knee joint injury and CAD after surgery
remain unclear. The decreasing volitional force output associated
with AMI and CAD may be caused by altered afferent input originating
from mechanoreceptors within the diseased joint reflexively which
reduce efferent output from quadriceps alpha motor neurons. Although
poorly understood, cortical pathways may also contribute to reduced
alpha motoneuron excitability.
Other factors such as joint effusion, pain, and disuse may
also contribute to quadriceps and hamstrings inhibition after
joint injury. The effused joint may reduce the excitatory input
of the surrounding muscles by activate several gating mechanisms
within the central nervous system (including both pre- and post-synaptic
inhibition). Joint effusion may also activate Ruffini endings,
which influence muscle tone and movement, by their influence
on Golgi Tendon Organ to
regulate joint stiffness and stability. Interestingly, pain-free,
experimental knee joint effusions with as little as 2030
ml of saline have been shown to produce quadriceps activation
Strength Training may help attenuate quadriceps and hamstrings
CAD. Rehabilitation progressing to high intensity can produce
greater quadriceps strength and attenuate CAD compared to lower
intensity rehabilitation. Training programs require intensities
of at least 3050% of maximal voluntary effort to overload
the muscle sufficiently to induce strength gains. This intensity
may not be possible in muscles effected with CAD and AMI. For
this reason, strength training alone does not seem to be an effective
modality for Quadriceps Activation Failure particularly for those
whose weakness is centrally mediated. Hurley et al reported that
a 4 week strength training therapy did not improve Quadriceps
Activation Failure in ACLd patients.
Other therapies aimed at removing posttraumatic AMI include:
- Manual therapy
- Transcutaneous electric nerve stimulation (TENS)
- Neuromuscular electric stimulation (NMES)
- Focal knee joint cryotherapy
Neuromuscular Electrical Stimulation
Electrical Musle Stimulation (EMS),
also known as Neuromuscular electrical stimulation (NMES), may
override AMI and CAD assisting in the restoration of quadriceps
muscle function and restore muscle mass more effectively than
voluntary exercise alone.
Early NMES treatment after TKA (before one month) may result
in better quadriceps function. Rehab can begin within 48 hours
after surgery and continue for several weeks. Protocols have
- twice per day sessions
- 15 repetitions per session
- biphasic waveforms at 50 pps
- 250 s pulse duration
- duty cycle 15 seconds on and 45 seconds off
Less frequent NMES application after surgery or injury (2
times/week) has not been effective even with a minimum 30% treatment
dose. High intensities result in greater gains in strength and
hypertrophy if used for a sufficient length of time, however
these higher intensities are often uncomfortable for patients.
Larger electrodes have a lower current density and, thus, may
decrease patient discomfort compared to smaller electrodes. Current
density is also influenced by the distance between electrodes,
with further distances resulting in lower densities and discomfort.
See EMS Unit
in ExRx.net Store.
Knee joint cryotherapy has been shown to improve quadriceps
function temporarily in those with AMI, thereby providing an
window of time to improve quadriceps muscle activation and strength.
Applying ice to the knee joint for 20 minutes before therapeutic
exercises results in greater strength gains compared either intervention
alone. In this particular application, cryotherapy does not undo
the damage to a joint, it only serves as a disinhibitory modality
to enhance motoneuron-pool availability during controlled rehabilitation
exercises. The goal of using cryotherapy is to provide a transient
period after application during which the resulting enhanced
quadriceps muscle function can be exploited.
Initiating therapy for Quadriceps and Hamstrings Activation
Failure early after injury or surgury is safe and achieves better
long term improvements in patient outcomes, rather than waiting
the deficit to resolve naturally
Hart JM, Pietrosimon B, Hertel J, Ingersoll CD (2010).
Quadriceps Activation Following Knee Injuries: A Systematic Review.
J Athl Train. 45(1): 8797.
Hart JM, Kuenze CM, Diduch DR, Ingersoll CD (2014). Quadriceps
muscle function after rehabilitation with cryotherapy in patients
with anterior cruciate ligament reconstruction. J Athl Train.
Stevens-Lapsley JE, Balter JE, Kohrt WM, Eckhoff DG (2010).
Quadriceps and Hamstrings Muscle Dysfunction after Total Knee
Arthroplasty. Clin Orthop Relat Res. 468(9): 24602468.
Thomas AC, Stevens-Lapsley JE (2013). Importance of Attenuating
Quadriceps Activation Deficits after Total Knee Arthroplasty.
Exerc Sport Sci Rev. 40(2): 95101.