SUMMARY

So what have we learned? Well we have been kind enough to give you a brief rundown  and take home message regarding the use of NMES for quadriceps strengthening during post-operative knee rehabilitation;

• Parameters; Biphasic/pulsed to maintain ROM, muscle re-education, preventing joint contractures or muscle atrophy, increasing blood flow, pain management and decreasing muscle spasm (best in early to intermediate stages), and Russian to improve muscle strength (best in intermediate to late stages).
• Dosage; according to the literature, to elicit strength gains in Quadriceps muscles post knee surgery (Russian parameter); 10-15min, 1x/day for 5 weeks, 15s:50s (on-off time) seems to be the general consensus.  For earlier/acute stages; ALARA.
• NMES contraindications/precautions (post knee surgery); Contraindications - musculotendinous lesion, absence of a secure bony attachment of the muscle, superficial metal, DVT, Infection.  Precautions - reduced sharp/blunt discrimination, broken skin.
• Increasing NMES frequency (>20Hz) does not increase muscle recruitment, it simply increases the rate of firing.  Lower frequencies minimize electrical fatigue, thereby improving effectiveness of treatment especially in acute stages.
• NMES is effective in increasing quadriceps strength in both impaired and unimpaired knees.  For optimal gains, NMES therapy combined with voluntary exercise produces significantly superior results.
• Younger and older populations benefit equally with short-term use, however in the long- term older populations may reap greater benefits as they are generally found to have diminished; baseline quadriceps strength pre/post surgery, motivation and adherence to rehabilitation relative to younger populations.  However, NMES in addition to high-intensity volitional exercise produces comparable positive results regardless of one's age. 
• NMES activates a similar proportion of voluntary capabilities and %MVIC in both sexes; therefore significant improvements in quadriceps strength occur postoperatively regardless of one's gender. 

Use of NMES in Young vs Elderly and Male vs Female

Ok guys, this week is our final post regarding the benefits of NMES on quadriceps strength. Today we are going to be discussing if there are differences/similarities between males and females, and additionally, if there are any discrepancies between the young and elderly.

Young vs. Elderly

Quadriceps Femoris (QF) muscle force deficits after TKA are a common occurrence and can prevent patients from returning to functional activities, especially in elderly populations due to impaired rates of healing.  Typically, but of course not in all cases, elderly populations tend to be less; active, intrinsically motivated and adherent to exercise/rehabilitation protocols compared to younger populations.  As a result, NMES may offer a potentially more effective means of increasing muscle force in specific rehabilitation reluctant populations/individuals.  For example, Lewek and colleagues (2001) established the following protocol for a 66-year-old man 3 weeks post TKA;

Number of sessions with NMES:	11
Additional exercises:	Stretching and high-intensity volitional strength program
Outcome (QF muscle force)	Involved versus Uninvolved:
3 weeks post TKA:	50%
8 weeks post TKA:	86%
10 weeks post TKA	93%

These values were also found to be similar for younger populations, proving that combining NMES with volitional exercise has equally beneficial effects regardless of age (Lewek et al., 2001).  Therefore functionally, patients are able to return to independent activities of daily living and recreational activities sooner than later.  Similarly, typically older populations as a result of either lifestyle (may also be the case for some younger individuals) and/or unavoidable degenerative changes may initially lack sufficient “baseline” strength prior to surgery, which becomes amplified 2-3 fold postoperatively.  Therefore these specific groups may benefit more and achieve greater gains from NMES treatment initially as they have a greater gap to make up compared to younger healthier populations (Lewek et al., 2001).  Therefore, their time spent using NMES may be markedly different and longer than the younger and typically more; active, intrinsically motivated, adherent and less muscularly deficient population groups.   In fact, studies have shown that patients experience less joint compression than isometric exercise groups, and overall less pain when NMES is used as an early stage strength producing modality specifically for the quadriceps (Laughman et al, 1983).  This as mentioned earlier is an important implication for patients suffering from degenerative joint diseases (Figure 1) or post total knee arthroplasty rehabilitation (http://www.youtube.com/watch?v=vdaipC-z9as).



Figure 1. Degenerative Joint Disease (DJD) of the knee

It’s similar to the concept of starting a 100 meter race from the 50 meter mark (younger, healthier populations with less quadriceps strength impairment pre/post surgery) versus the 0 meter mark (older, relatively less healthier populations with greater quadriceps strength impairments and time spent in rehab pre/post surgery); the more you start with initially the less you have to make up after the fact, therefore the less additional external support (NMES) required to see and make gains (in quadriceps strength).

Males vs Females

Straight away, the natural reaction would be to assume that men would achieve greater benefits to NMES than women. Why is that the case?

Simply, it is proven (or common knowledge) that the average male is generally stronger than the average female, as well as, having a larger overall muscle mass, and a higher tolerance to fatigue (arguable)!

So what does the literature reveal?

Laufer and colleagues (2010) established the physiological response to NMES may be determined by the intrinsic tissue properties of the individual, including the following.

• According to Petrofsky et al (2009) subcutaneous fat directly hinders the transfer of current into the tissue, therefore, possibly affecting force of contraction.
• Men generally have a higher amount of muscle mass and a lower portion of adipose tissue to women. Therefore, possibly effecting the stimulation of muscle and the overall strength.

Additional findings include:

• Studies by Bergman et al (2001) have revealed differences between males and females, in terms of tolerance to current intensity (CI). They established that male subjects had a strong tolerance to higher CI’s, which resulted in stronger contractions. However, when measured as a percentage of a maximal voluntary isometric contraction (%MVIC), there was very little difference between genders.

Ultimately, literature demonstrates physiologically men should receive greater outcomes, in the use of NMES over women.  Is this true?

A study done by Laufer et al (2010) looked at the response of male and female subjects performing repeated NMES of the quadriceps femoris muscle, post total knee arthroplasty (TKA). The following was identified:

• Electrically induced contractions in the majority of patients were within the therapeutic range of 25%-50% of MVIC.
• Men demonstrated stronger voluntary and maximal electrical induced contractions (MEIC).
• Men tolerated higher CI’s
• There was no gender differences in %MVIC
• All force measures (both men and women) increased significantly across time
• All subjects demonstrated a common trend of habituation to CI

Therefore, it is clear NMES activates a similar proportion of the voluntary capabilities for both males and females, which ultimately, elicits quadriceps contraction within the range suitable for muscle strengthening.

NMES combined with a voluntary exercise program

 

Hello again everybody.

Well, we hope you all have been learning over the course of our discussion. This next topic we are going to discuss is the crux of our investigation. We are comparing the use of NMES (post surgery) on quadriceps strength combined with a voluntary exercise program. The evidence supporting this discussion was viewed around subjects who either had Anterior Cruciate Ligament reconstruction (ACLR) or Total Knee Arthroplasty (TKA).

So let’s dive right into the information.

Although specialists continue to make efforts towards improving current rehabilitation techniques and developing new interventions to maximize quadriceps output following ACLR/TKA, a universally effective approach by which to restore pre-injury muscle strength has not been revealed (Palmieri-Smith, Thomas et al. 2008). So where does that leave us?

Well, we have established there is no exact method of rehabilitation, however, there are a variety of techniques that have established significant results, and additionally, there is marketable evidence that supports the use of NMES in combination with voluntary exercise.

The primary objective of a post ACLR or TKA is to provide a rehabilitation program that restores knee function to its optimum level. These objectives/goals are a challenge, as many patients return to sport or Activities of Daily Living (ADL’s) with persistent neuromuscular deficits, which ultimately include:

·    Quadriceps weakness (being the most common)

6 months post ACL surgery, quadriceps strength can diminish by 20%, which is a major deficit for an athlete returning to a competitive level of sport (Palmieri-Smith, Thomas et al. 2008).

So why does this happen? According to Palmieri-Smith and colleagues (2008) there are two underlying reasons, which include:

Figure 1: Demonstrates muscle
atrophy in the (R) quadriceps

·    Muscle atrophy, which is due to lack of use.

·    Arthrogenic Muscle Inhibition (AMI), which simply refers to voluntary muscle activation failure

o    Specifically, the decrease in mechanoreceptors from the ACL affects the reflex activity between the ligament and the quadriceps, resulting in an inability to actively recruit high-threshold motor units during voluntary quadriceps contraction.

With the use of NMES, the goal for rehabilitation is to target AMI. How is this done?

·    NMES directly activates the motor axon and recruits the inhibited motor neurons

·    Additionally, a greater number of Type 2 muscle fibres are generated which produce a greater force production in the quadriceps muscle

So what does the literature reveal about ACLR and TKA and the use of NMES as an adjunct treatment for rehabilitation?

A study by Synder-Mackler and colleagues (1995) established that four weeks of high intensity electrical stimulation combined with active exercises resulted in the following;

·    70.1% quadriceps strength at 2 months post reconstruction

·    Subjects who performed only voluntary exercises only demonstrated 46.7% quadriceps strength

In addition Delitto et al (1988) reported the following findings at 8 weeks post ACL surgery:

• Subjects receiving NMES therapy had an isometric quadriceps strength of 78.8%
• The active exercise group only produced an isometric strength of 51.7%

Additional findings to Synder-Mackler and collegues (1995) revealed an Improvement in functional outcomes, including:

• Patients who had received NMES walked with a faster cadence and velocity
• A more functional knee flexion excursion

Therefore, it is clear that existing literature supports that NMES combined with active exercise is more effectual than active exercise alone in the restoration of quadriceps muscle (Palmieri-Smith et al, 2008).

There are some pit falls to the use of NMES in these studies. According to Fitzgerald et al (2003) one of the major concerns is that patient’s struggle to tolerate the protocol. The underlying reason for this is that some patients had undergone patellar tendon auto-graft ACLR, which  specifically effected the position the knee is placed in during treatment (flexed between 60 and 90 degrees), whilst being connected to a dynamometer (measures force/power). As a result, Fitzgerald and colleagues (2003) produced a modified NMES protocol. The general protocol used can be seen in our first blog. The protocol used by Fitzgerald and colleagues (2003) involved placing the knee in extension, not connecting the patient to a dynamometer (reduces set-up time), as well as modifying the stimulus amplitude.  The amplitude was increased till a full tetanic contraction of the quadriceps was evident, with an additional superior patella glide. At this point the amplitude was increased to the patient’s maximal tolerance level. All other parameters were consistent with traditional methods as seen in blog 1.

So, what results were produced with this modified protocol?

• NMES patients revealed a higher quadriceps index compared to the exercise group
• NMES group demonstrated higher ADL’s at both 12 and 16 weeks post surgery
• NMES subjects (at 16 weeks) achieved the clinical criteria to advance to agility training exercises compared to the active exercise group (Fitzgerald, Piva et al. 2003).

Evidently, this literature reveals that there can be slight complications with the application of NMES, however, as Fitzgerald and colleagues (2003) demonstrate there are ways of modifying (advocating for your patient s) the application of NMES whilst reaping the full benefits of the treatment.

Currently, the question researchers ask is; how long does the quadriceps strength gain last once NMES treatment has concluded? Simply, the research reveals that there is still considerable strength in the short-term (first 4 to 8 weeks), post ACLR treatment, but long –term still requires more investigation. However, a study by Steven et al, (2004) looked specifically at the benefits of NMES post TKA and established that quadriceps strength gains were still present at 6 months following treatment.

In summary, to maximize quadriceps strength, specialists need to incorporate methods to reduce muscle atrophy and AMI. If these factors can be reduced quickly following ACLR/TKA a more successful and efficient recovery will transpire for patients. Overall, we can see from the evidence provided that NMES therapy (traditional or modified protocol) combined with voluntary exercise, for post ACLR/TKA rehabilitation is a beneficial modality to increase quadriceps strength.

Stay tuned; next week, for our final post, we’ll be comparing the use of NMES in different aged populations (young and old) and the differences in benefits/affects between male and females.

Thanks for tuning into this week’s discussion, we hope you all enjoyed it and we’ll see you again next week.

NMES versus No exercise: Beneficial effects?

Hello again everybody! As promised, this week we will be talking about the use of NMES to strengthen normal skeletal muscle without voluntary muscular effort.  Can this in fact be true?  To answer this week’s question, we investigated some literature out there that looks to support the application of NMES for muscle strengthening, more specifically can it provide benefits that outweigh doing no exercise at all?

Laughman and colleagues (1983) used NMES to investigate its effect on Quadriceps Femoris (QF) strength over a 5-week period without superimposed voluntary contractions.  Their parameters were as follows (Table 1);

Frequency:	2500Hz (Russian)
On/Off time:	15s:50s
Times/day:	10
Days/week:	5
Total weeks of treatment:	5
Total Sessions:	25
*All participants were asked to maintain regular daily activites*

Table 1.  Treatment parameters established by Laughman and colleagues (1983).

So what did they find? Essentially, where the control and isometric groups experienced increase in strength gains of 2% (attributed to the evaluation process) and 18 % respectively, the NMES group had a statistically significant 22% gain over the 25 training sessions.  Other significant findings include;

• Patients tolerated progressively increasing amounts of current density, indicating muscle accommodation consistent with strength gains.
• Support for cross-education effect on muscle strengthening via neural effects, which were originally only thought to be possible by voluntary muscle contraction.
• Rapid strength gains in first few weeks with slight plateau achieved in weeks 4 and 5.  Overall, from weeks 1-6, NMES alone had a greater effect that isometric exercise group.
• Patients experienced less joint compression than isometric exercise group, and overall less pain.  Important implications for patients suffering from degenerative joint diseases or post total knee arthroplasty rehabilitation for QF strengthening.

NMES slows the biochemical and histological (Figure 1) changes that accompany disuse muscle atrophy (Figure 2) after major surgery.

Figure 1.  Histological changes within Type I and II QF muscle fibres pre (left) and (post) knee surgery.  

Figure 2.  Disuse Quadriceps muscle atrophy in right (normal) versus left (affected) thigh.

• Important function of NMES to strengthen weak muscle groups or by providing a passive intermittent stretch to shortened joint soft tissue preoperatively.
• Recommended treatment prescription to elicit strength gains in Quadriceps muslces; 10-15min, 1x/day for 5 weeks with frequency and on/off time as described in table 1 above.

Additional Findings;

• Significantly better results in NMES versus no-exercise groups as tested by Bax and colleagues in 2005 (support for NMES for Quadriceps strengthening even 22 years after initial testing).
• Increase in vertical jump height in healthy basketball players (NMES applied to Quadriceps); 4.9cm increase for squat jump, and 0.3cm for countermovement jump (Bax et al., 2005).
• Patient and electrode positioning/size (http://www.medco-athletics.com/lectureseries/neuro.html); no significant differences in-patient with knee in flexion (Snyder-Mackler Approach) versus extension (Fitzgerald Approach).  However, most experts have supported flexion because Quadriceps muscles are placed in a more relaxed/lengthened position therefore allowing for greater muscle range and overall force generation (Fitzgerald et al., 2003).   

So as we can see from the evidence presented, NMES can in fact be an effective modality to increase quads strength in both impaired and normal knee function populations when compared with no exercise and even isometric exercise.  Next week we will be going more in depth with a look at the use of NMES for maximizing quadriceps strength following knee surgery (mainly ACL reconstruction and TKR).  Our main focus will center around two key areas of discussion/comparison;

1.    Volitional exercise versus NMES

2.    Combined volitional and NMES

Hope you all enjoyed this weeks post, SEE YOU NEXT WEEK!!!

Hey Cath thanks for your post!

With regards to your inquiry regarding the discrepancy that exists between our listed frequency of 75Hz versus the idea that the frequency should be low in order to minimize early onset of fatigue, we did some follow-up on that and found some interesting evidence.  But before getting into the early onset of fatigue, does low versus high frequency NMES illicit different effects?  As we know, results regarding the effectiveness of NMES vary due to the wide range of parameters that can be adjusted and customized.  These range from the frequency, intensity, impulse width, on/off times, number of electrodes and electrode placement.  In a study conducted by Rebai and colleagues (2002), they looked specifically at the effects of two NMES frequencies in the thigh muscle after knee surgery in order to evaluate any differences in recovery.  Their NMES parameters were setup as follows;

	Group 1: 20Hz	Group 2: 80Hz
Pulse Duration:	300 microseconds	300 microseconds
On/off time:	15s/10s	15s/75s
Treatment time:	60 minutes	54 minutes
Voluntary exercises:	Both groups given same standard exercise program.  2 hours of voluntary exercise and 1 hour of NMES per rehabilitation session.
*Number of impulses were standardized for both groups*

 

Results of their study revealed that quadriceps peak force, specifically Quadriceps Femoris (Figure 1) strength, for the 20Hz group had better results in the operated versus non-operated limb, although some studies refute this finding stating that no significant differences exists between the low and high frequency settings (Bax et al., 2005). The 20Hz group recovered ~93% of thigh muscle volume versus ~89% for the 80Hz group thus indicating less atrophy (in both type I and II fibers).  Furthermore, subcutaneous fat measurements were found to be significantly higher in the 80Hz group.  Why is this important?  For two reason; 1. Fat acts as an insulator in the body, it blocks/acts as a barrier against the electrical impulses reaching deeper tissues emitted by the NMES device thereby reducing its effectiveness.  2. Greater accumulation of subcutaneous fat reveals that the area is not being worked very hard, which supports this studies first finding that the 20Hz group gained more strength as a result.

Figure 1.  Quadriceps muscle group - Quadriceps/Rectus Femoris highlighted in red.  

 

 

 

Now getting back to the original question regarding muscle fatigue with low versus high frequency, increasing frequency does not increase muscle recruitment; it simply increases the rate of firing. Therefore, in protocols that have little rest time and longer durations of stimulation (as outlined by Rebai and colleagues) lower frequencies are selected to minimize electrical fatigue of muscles and improve effectiveness of treatment as the results demonstrate above.