CASE STUDY: Lower Extremity Neuromuscular Deficit Testing & Impact on Functional Training

Neuromuscular deficits can persist long after an injury. They have been attributed to a lack of muscle fiber recruitment as well as a lack of cortical (brain) and spinal excitability.¹ mTrigger’s Neuromuscular Deficit Test measures the neuromuscular activity and function of the impaired limbed compared to the uninvolved limb. Abnormal movement patterns are very common after surgical intervention or injury, and, furthermore, they are not always isolated to the injured side; therefore, gaining a full clinical picture is critical to recovery.

The case study below shows us several different ways neuromuscular deficits can play out during functional movement and what that means clinically. Let’s explore how functional movement impacts bilateral deficits in the quads, hamstrings, and glutes.

Background

While isokinetic testing (such as a Biodex) plays a role in rehab and return to play decisions, it is certainly not the whole picture. Many studies have shown that athletes cleared to play continued to demonstrate abnormal movement patterns and characteristics over a year after injury.² Movement asymmetry has been attributed to primary and secondary ACL injuries, as well as a variety of other injuries, and symmetrical movement and strength patterns are common criteria for medical discharge and return to sport.2  So, how do we take a more critical approach to assessing movement patterns? Studies show that biofeedback techniques can help patients to relearn and optimize desired movement patterns³ – and this is where mTrigger comes into play. 

Measuring Strength Deficits

Let’s go through a few ways mTrigger sEMG biofeedback can be used to access deficits and optimize movement coordination while performing functional tasks.

1. Begin by measuring the neuromuscular strength deficit under the “NEUROMUSCULAR DEFICIT TEST” module. This protocol gives an objective measure from which to start. In this first video, we see an example of neuromuscular strength deficit testing for the quadricep muscle.
2. Using Dual Channel mode, place the electrodes on the quadricep muscle: channel 1 on the involved side, channel 2 on the uninvolved side.
3. Instruct patient to perform the isolated exercise (in this case a single leg squat) for 30 seconds (3x 5-second reps) on each side.
4. At the end of the session, a neuromuscular deficit percentage is provided. A negative percentage indicates that the involved side is actually activating at a higher level than the uninvolved side. 

For this patient, the involved side (LEFT) is 2% weaker than the uninvolved side (RIGHT). This gives us great information to utilize when developing a training program. Furthermore, this deficit can be reassessed later to track and show progress.

Functional Application – Back Squat

Now let’s look at how this deficit manifests during functional exercise.

1. 1. Select a functional exercise that targets the desired muscle group. In this case, a back squat was selected to assess the difference in quadricep muscle activation.
      1. Using dual channel mode, place channel 1 on the affected side and channel 2 on the unaffected side.
      2. Under the “Train” setting, instruct patient to perform a squat at a slow and steady pace for the duration of the exercise. (Remember: you can edit exercise timing parameters under Settings to match your desired pace and duration for that exercise)
      3. As the patient performs the exercise, they are instructed to increase the muscle activation of both meters equally and simultaneously.
      4. At the end of the exercise duration, click “SAVE SESSION”.
      5. Now, go to the “TRACK” section and select the most recent session for both channel 1 and channel 2.
      6. Lastly, tap on the graph for each channel. This allows you to move back and forth between the graph (to show performance over the duration of the exercise) and average MVC for each channel during the exercise.
         
         

In this case, the average MVC for the involved side (Channel 1- LEFT) was 868 microvolts, and the average MVC for the uninvolved side (Channel 2 – RIGHT) was 869 microvolts.

When calculated out, our functional squatting deficit in this instance was less than 10%. In fact, it was almost equal. This is affirmation that a subtle weight shift is not occurring, and the athlete is performing the exercise equally. However, let’s take a look at how this deficit progresses when weight is increased.

Weight          Involved Side (L)         Uninvolved Side (R)        Deficit
Light                             868                                          869                                 0%
Medium                       922                                           851                                 -8%
Heavy                           945                                          825                                 -14%

In this case, the side measured with a 2% neuromuscular deficit is activating at a comparable level with exercises performed bilaterally. In fact, it is activating better than the uninvolved side and increases activation with increased weight. Clinically, this is good news, however it points towards the importance of more unilateral exercises. For this patient, the MVC provided by mTrigger allows the clinician to progress weight safely without feeding into compensation patterns.

Hamstring Deficit

Let’s looks at a similar example with the hamstring.

1. Begin by measuring the neuromuscular strength deficit of the isolated hamstring muscle under the “NEUROMSUCLAR DEFICIT TEST” module. In this first video, we see an example of neuromuscular strength deficit testing for the hamstring muscle.
2. Using Dual Channel mode, place the electrodes on the hamstring muscle. Channel 1 goes on the involved side, channel 2 goes on the uninvolved side.
3. The patient is instructed to perform the isolated exercise, in this case a single leg bridge with heel dig, for the NMDT protocol.
4. At the end of the session, a neuromuscular deficit percentage is displayed.
   
   

In this example the involved side (LEFT) is 12% weaker than the uninvolved side (RIGHT). This gives us an objective measure we can use to track and show progress. 

Functional Application – Deadlift

Now, let’s take a look at how this strength deficit plays out when performing a functional deadlift exercise:

Weight          Involved Side (L)         Uninvolved Side (R)        Deficit
Light                             525                                          604                                 13%
Medium                       779                                           910                                 14.4%
Heavy                           929                                          946                                 1.8%


Although the deficit measured during functional activity is similar to the deficit measured during neuromuscular deficit testing, when weight is added, the deficit diminishes. As the demand for muscle activation increases with the added weight, we see an increase in hamstring muscle activation levels to meet the demand of the task. In this case, continuing to perform heavy weight training in addition to unilateral exercise is safe and indicated.

Glute Deficit

Finally, we looked at the neuromuscular deficit of the glutes.

1. Begin by measuring the neuromuscular strength deficit of the glute (max) muscle under the “NEUROMSUCLAR DEFICIT TEST” module. This video shows an example of neuromuscular strength deficit testing for the glute muscle using a hip lift.
2. Using Dual Channel mode, place the electrodes on the glute max muscle: channel 1 on the involved side, channel 2 on the uninvolved side.
3. The patient is instructed to perform the isolated exercise, in this case a hip lift, for the NMDT protocol.
4. At the end of the session, a neuromuscular deficit percentage is displayed.

In this example, the involved side (LEFT) is 11% weaker than the uninvolved side (RIGHT). 

Functional Application – Deadlift 

Using the same functional deadlift exercise, let’s see what happens to the neuromuscular deficit of the glutes.

Weight          Involved Side (L)         Uninvolved Side (R)        Deficit
Medium                        344                                         335                                -2.6%

Despite having a small strength deficit during testing, the glutes perform quite well from a bilateral standpoint in this exercise. The deficit is negative, indicating that the left side actually has a slightly greater output than the uninvolved right side. Based on this information, the glutes are activating well during this exercise. Although they should continue to be challenged in other ways, the glutes don’t need to be the main focus of cueing and biofeedback during this exercise for this patient. 

Summary

Biofeedback has the ability to provide real time performance indications that can assist athletes with overcoming neuromuscular strength deficits throughout their rehabilitation process. When used appropriately, biofeedback has the integral ability to refine and optimize the movement patterns of athletes looking to return to sport and high-level function.

Measuring strength deficits is critical for tracking objective progress and making return to play decisions. Using mTrigger’s Neuromuscular Deficit Test and Train/Track functions, you can gather and track progress over the course of treatment. Furthermore, mTrigger allows you the flexibility to functionally measure and compare how neuromuscular deficits manifest in common movement patterns. This information is critical for optimizing movement, enhancing recovery, and making smart, safe return to play decisions.

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References

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