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.