Strength, But Not Muscle Mass, Is Associated with Mortality

As we age, both the size and strength of our muscle declines from disuse, resulting in an increase in functional limitations. It would make sense that these two factors play a role in increasing risk of mortality due to their effects on overall function, but muscle strength may have a more association with mortality than you’d expect. In a recent study published in the Journal of Gerontology by Newman et al., the ratio of muscle size to strength was examined in relationship to mortality along with a host of other factors. 

This study included 3075 healthy men and women aged 70-79 surveyed every 6 months with total mortality being assessed over a span of 6 years. Two main variables were of importance in this study – measurements of muscle mass and body composition which were taken via imaging (CT, DXA), and muscle strength which was measured via grip strength and knee extension (quadriceps) strength. The study also looked at other variables that may affect the strength-mortality association including age, race, physical activity, chronic conditions, and smoking.

What the study found, is that low muscle strength (grip and quadriceps) alone can, in fact, be a predictor of mortality in both men and women. Measurements of muscle mass did not play a role in this relationship and even when accounting for variables such as chronic illness or physical inactivity, this association between strength and mortality can still be seen. Future research is needed to uncover the underlying cause for this strength-mortality association, but until then perhaps we need to be paying closer attention to grandma and grandpa’s handshake!

How test specific is strength?

Generally, when you work out you expect to get bigger muscles and become strong. But, do we necessarily need to perform rep after rep in order to see the same strength gains, or can just practicing a specific exercise give us similar results? In a recent study published in Medicine & Science in Sports & Exercise, Mattocks and colleagues explore this concept of specificity. 

In this study, 38 untrained participants between the ages of 18-35 performed both a knee extension and chest press exercise twice a week for 8 weeks. Participants were assigned to one of two groups, a high-volume training group that completed what we would consider a regular gym regimen of 4 sets of 8-12 RM, or a test group that performed their 1RM up to 5 times. At each training session, the participants were asked to rate their “perceived recovery” on a scale of 0-10.

To measure changes in muscle strength, size, and recruitment between the two groups, this study compared pre and post values for 1RM, muscle thickness (via ultrasound), isokinetic & isometric strength, electrical activity in the muscle (via sEMG) and muscle endurance. As you would expect, the group that performed a higher volume of exercises saw an increase in muscle thickness and muscle endurance due to the low load high rep nature of this training regimen. Unexpectedly, this study found no between group differences in isotonic or isometric muscle strength for chest press or knee extension. Of note, the group performing the 1RM saw no increase in muscle size, but did see increases in strength equal to the high volume group.

Although this study is limited due to its short nature, the concept it introduces may change the way we think about strength training. Increases in training volume and muscle size may not be the perfect recipe for strength gains. It turns out bigger may not always be better. 

Effect of Anodal Transcranial Direct Current Stimulation of the Motor Cortex on Elbow Flexor Muscle Strength in the Very Old

As we age, it is typical to see a decline in strength due to a loss of muscle mass, or atrophy, but recent evidence suggests our nervous system may also play a role in this via a decline in motor cortex excitability. With a continual decline in strength comes increasingly more functional impairments in mobility and increased risk of injury in the very old. The question is, how can we can manage these neural changes to diminish the effect they have on strength and function in older individuals? In a recent study published in the Journal of Geriatric Physical Therapy by Oki and colleagues, this question is explored further.

Oki and colleagues proposed that the use of transcranial direct current stimulation (tDCS) of the motor cortex may have positive effects on muscle strength and voluntary activation in the very old population. Their study involved 11 participants (>80 years old) completing isometric strength testing of the non-dominant elbow flexors on 3 separate occasions. The first session was to establish a baseline, the second was performed following tDCS or imitation tDCS for 20 minutes, and the last was to compare for any significant difference. In addition to measuring strength, each session included examination of electrical activity within the muscles (EMG) as well as voluntary activation (via electrical stimulation).

Surprisingly, the results of this study did not confirm researcher’s hypotheses. There was no significant difference between anodal tDCS and imitation tDCS on strength, electrical activity (EMG) or voluntary activation. The thought was that by increasing voluntary activation, there would be a resultant increase in strength and electrical activity (EMG amplitude) in the muscle. Instead, what they found was that there weren’t really any limitations in elbow flexor voluntary activation. In fact, on average participants showed 99.3% voluntary activation levels of the elbow flexors. With there already being such high voluntary activation, the use of an outside mechanism to further increase that number was unrealistic. With that being said, it is possible that you may see more significant effects of anodal tDCS in musculature with lower voluntary activation levles, but this is just one of several limitations of this study. All in all, the most surprising outcome of this study was how efficiently 80+ individuals were able to recruit their muscles when asked to!   

Mental Imagery and Muscle Strength

Strength is often associated with muscle mass. When we picture strength, we picture a bodybuilder or football player – someone with big muscles. What we less often associate with strength, is its connection to the brain. There are “neural factors” that play a role in muscle performance. For example, in order to get a muscle to fire, motor units must be recruited systematically to produce the action you want. So what happens if our muscles can’t produce any action? Following an injury that requires immobilization, the muscle goes through a period of disuse and becomes weak. Part of this loss in strength occurs as a result of the decline in physical work or motion at the level of the muscle, but recent studies suggest there may also be a neurological component that we can target in order to minimize weakness following immobilization.

This concept was explored in a recent article published in J Neurophysiol by Clark and colleagues. The aim of their study was to determine whether or not the motor cortex plays a role in regulating muscle strength/weakness following immobilization-induced loss of strength via mental imagery (MI). In this study, 29 healthy participants were immobilized at the wrist and hand for 4 weeks, and 14 of those participants performed MI exercises 5 days/week. Measurements of isometric muscle strength, voluntary activation, and silent period during 15% max voluntary isometric contraction were recorded at baseline, immediately after immobilization, and 1 week after immobilization. Mental Imagery exercises consisted of participants performing 52 imagined contractions of the wrist flexors, initiated by commands such as “imagine that you are pushing in against a handgrip as hard as you can.” To get an idea of the degree to which MI effects post-immobilization weakness, results were compared to a control group that did not complete any visualization exercises during the 4-week immobilization.

Interestingly enough, MI was proven to be highly effective in reducing loss of strength and voluntary activation by 50% following immobilization when compared with the control group. Although details of the mechanism may not be clear, is is clear that MI in some way reduces cortical inhibition (by activating areas in the motor cortex), thereby limiting loss of strength. Based on these findings, it may be time we start looking at strength with a broader lens, with consideration of this neurological component. From a clinical standpoint, this study highlights mental imagery as a potential treatment option during periods of immobilization to reduce the detrimental effects that disuse can bring after the fact. 

Sarcopenia and depression: is there a link?

Many elderly individuals experience a natural loss of muscle mass and strength, also known as sarcopenia, as they age. In addition to a decline in physical functioning, aging also seems to impact psychological functioning, with higher rates of depression in older individuals. Several studies have begun to look at the incidence of sarcopenia and depression in this population, and are finding that it is not uncommon to see both. The big question is, do sarcopenia and depression just share common risk factors, or is there a more direct link between the two? Ke-Vin Chang and colleagues recently published a review in Age and Ageing that aimed to answer this question. Researchers evaluated at 15 observational studies primarily involving individuals over 50 years old, with women accounting for a little over half of the participants. Information compared from each of the studies included study type, participant characteristics, methods of body composition measurement, diagnostic tools for sarcopenia & depression, and relevant variables that may have affected the relationship between sarcopenia and depression.

The authors found that there is in fact a positive association between sarcopenia and depression, even when controlling for factors such as BMI, gender, age, chronic comorbidities (diabetes, cardiovascular disease), and physical performance. Meaning, that although these two conditions do share several common risk factors, there is perhaps a more direct link. It should be noted that further studies are necessary to determine an underlying cause between the sarcopenia and depression, and whether or not there is a biological component that is truly responsible.   

Interpretting Fatigue Data: Methods Matter!

A well-researched topic in the Exercise Science world is muscle fatigability due to its relevance in the athletic population in regards to increased risk of injury. Numerous studies have attempted to quantify fatigue using various methods, but there is a gap in research regarding which method most accurately depicts this decline in strength as it relates to torque production. In a recent study published in The Open Sports Sciences Journal by Ciccone and colleagues, they attempt to fill this gap by examining how the method used effects data interpretation and which methods seem to be best.

In this study, 18 healthy males and females performed 50 maximal effort knee extensions using an isokinetic dynamometer (Biodex). Participants were familiarized with how the machine works, and practiced performing knee extensions from 90° knee flexion to 180° (full extension) prior to the experimental trial. Fatigue was measured using two methods – calculation of a fatigue index and calculation of torque slopes. Fatigue index was calculated using the following equation: [(initial torque – final torque)/initial torque]x100. Initial torque was selected from one of the following values: average of first 3 reps, average of first 5 reps, highest 3 rep average, or highest 5 rep average. The final torque was selected from either the last 3 or last 5 reps. Data was collected over 30 reps and 50 reps, because of the commonality of these two values in research. Both isokinetic load range and the angle at which peak torque is produced was recorded for each trial.

This study produced several outcomes of interest, mainly confirming the complexity of measuring muscle fatigue as it relates to torque production and the multiple variables you must consider. Firstly, depending on which torque variable you use (initial, end, peak etc) you will get varying calculations of fatigue index. Rather than using the first 3 reps which would lead to an underestimation of fatigue, this study found that using the peak 3 or peak 5 reps provided a much better representation of decline in strength. In addition, instead of estimating a potential range of motion in which its most likely the individual will produce maximum torque, this study found it’s better to look at torque throughout the full range of motion due to the variability in knee angle at which peak torque production occurs especially with fatigue. Lastly, studies that look at slope of torque to measure fatigue should focus on repetitions following the rep at which peak torque was produced, instead of focusing on the first few reps in order to avoid underestimating fatigue.

Looking at the big picture, perhaps we need to be more consistent and precise about which methods are used in research examining muscle fatigue and force production via isokinetic dynamometry so that the data we interpret is reliable enough to draw conclusions from and incorporate into our clinical judgement as it relates to high level athletes.

Does a placebo still work if you know it is a placebo?

Chronic low back pain is an extremely common problem for individuals worldwide, leading to frequent feelings of disability. There are many pharmaceutical drugs patient’s use for chronic low back pain, but their effectiveness seems to be limited at times. Interestingly enough, recent research has shown that placebo treatments may have utility in managing chronic low back pain. Carvalho and colleagues recently published a study in Pain that aimed to examine patient outcomes using treatment as usual (TAU) and TAU with the addition of placebo pills. The study included participants 18 years or older that have had persistent low back pain for over 3 months. Participants were randomly put into 2 groups – an experimental group and a control group that would resume treatment as usual with the option of taking placebo pills at the end of the study. All participants were educated on what a placebo pill is, and the possible effects it can have on their body.  The experimental group took 2 pills twice a day for 3 weeks. Patients rated their pain on a Numeric Pain Rating scale from 0 (no pain) to 10 (worst pain imaginable) before the start of the treatment, midway and at the end. Measurements for maximum, minimum, and usual pain were recorded. In addition to measuring pain, participants filled out the Rolland-Morris Disability Questionnaire to give researchers an idea of what difficulties they were having on a daily basis with a higher score indicating a higher level of disability.

Given that the participants were fully aware of the placebo pills, you would expect that the treatment would not be as effective. Interesting enough, this study showed just the opposite. Overall, the placebo group reported greater pain reduction on each of the 3 pain rating scales as well as a decrease in pain-related disability compared to treatment as usual. Even the participants that voluntarily took placebo pills following treatment as usual experienced significant pain relief and decreases in pain-related disability. In fact, 17 participants requested a prescription for these placebo pills to treat their chronic low back pain at the end of the study! The mind is a powerful thing!  

Metabolic risk in kids- the important distinction between active versus active and strong

Most parents, teachers, and clinicians would agree that it's important for children to be active. But, what about muscle strength? When it comes to risk factors for metabolic diseases such as type II diabetes, is there a distinction to be made between active and strong? An interesting study by Gomes and colleagues published in the American Journal of Human Biology tried to tackle this issue. The researchers studied 378 Portuguese children between the ages of 9-11 years. Physical activity was assessed for a seven day period, and muscle strength was tested via handgrip dynamometry (normalized to body weight). The children were divided into low and high physical activity and strength groups using the 50th percentile scores as cutoffs. Each child's metabolic risk was computed from waist circumference, blood pressure, cholesterol, and blood glucose measurements. Not surprisingly (and sadly), 65% of the children were classified as inactive. Interestingly, the researchers reported that the children with the highest muscle strength had the lowest metabolic risk, even after adjustment for physical activity. In addition, there were important differences among the groups of children, such as lower waist circumference and metabolic risk for the active + strong group compared to the active + weak group.

Although the work of Gomes et al. (2017) was not without some limitations, these findings suggested that muscle strength is an important predictor of metabolic health in children. Moreover, a distinction can be made between kids that are both active and strong compared to just active.

Can musculoskeletal ultrasound be used at the bedside in the ICU to predict adverse outcomes?

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Ultrasound is being increasingly utilized by researchers in the areas of exercise physiology, biomechanics, and rehabilitation science. Part of the reason for this is its portability and ease of use. It hasn't necessarily been adopted by clinicians in hospital settings, however. Recent work by researchers at Harvard Medical School may change that. The study, published by Mueller et al. in Annals of Surgery, sought to determine if muscle size of the rectus femoris was able to provide similar predictability as the Frailty Index Questionnaire, which is a 50 item survey assessing attributes like independence, social support, and depression. 102 critically ill patients completed the study. Upon admission in the ICU, muscle cross-sectional area of the rectus femoris was determined and the patients completed the Frailty Index Questionnaire. The authors found that the muscle size measure and the questionnaire were equally effective in predicting whether a patient would be discharged to a skilled nursing facility versus in-hospital mortality. All of the patients that died in the hospital had been classified as sarcopenic based on the ultrasound data. The researchers concluded that ultrasound used at bedside during admission in the ICU was as effective as subjective assessment of frailty. The advantage of ultrasound, however, is that it is simple to perform and does not require cooperation from the patient.

Does a history of strength training prevent muscle weakness during short-term disuse?

A number of studies have demonstrated that disuse of a muscle group results in significant muscle weakness. Until recently, however, it wasn't clear if chronic strength training was protective against strength loss. Deschenes and colleagues recently published some very important work in the American Journal of Medicine and Rehabilitation. Eleven men with a history of strength training (average = 5+ years) and 11 control participants completed the study. Both groups had their knee joint immobilized for 7 consecutive days and used crutches to get around. Muscle strength and mass, as well as several other neuromuscular variables, were measured before and after the 7 day period. Interestingly, the authors found that both groups got significantly weaker as a result of their disuse. Muscle activation was higher for the trained participants at both pre and posttesting, but other variables were not affected by the intervention. It was therefore concluded that a history of chronic strength training did not prevent muscle weakness. 

It is important to point out that the trained group was still roughly 50% stronger than the untrained participants after the 7 day period. At the end of the study, the strength of the trained group was substantially higher than the pretest values for the control group. Thus, the participants' strength training background was still beneficial in the sense that the trained group had a much greater capacity for change. Put another way, when a muscle group is weak and an unexpected situation requiring disuse of a joint occurs, there isn't much further down to go!

Observation of Limb Movements Reduces Phantom Limb Pain in Bilateral Amputees

Phantom limb pain (PLP) is an extremely common problem for individuals following the loss of a limb. Although the pathophysiology behind this sensation isn’t completely understood, there are treatments that have proven to provide patients with some relief. Currently, one of the most beneficial treatments for individuals with unilateral limb loss is mirror therapy.  The basic idea behind mirror therapy is that by observing the motion of their intact limb, they may visualize movement of their phantom limb and experience pain relief. This may work for unilateral amputees, but what about bilateral amputees? How can we help them?

A recent study published in ANNALS of Clinical and Translational Neurology by Tung and colleagues may have found a potential treatment option for this population. Their study included 20 male bilateral amputee patients with at least 3 episodes of phantom limb pain per week rating at least 3/10. Subjects were placed into 1 of 2 groups – either direct observation or mental visualization with 20 min treatments daily for one month. In the direct observation group, participants observed lower extremity movements and mimicked them with their phantom limb. In the mental visualization group, participants were asked to visualize themselves moving their phantom limb and feet. In order to measure improvements in PLP, this study used a 0-100 visual analog scale as well as the Short Form McGill Pain Questionnaire and asked subjects about episodes & duration of PLP since last visit.

Similar to studies for PLP relief in unilateral amputees, this study found visual treatments involving direct observation to be very effective in bilateral amputees. The direct observation group showed significant decreases in phantom limb pain on both the visual analog scale and Pain Questionnaire, whereas the mental visualization group showed no decreases in phantom limb pain on either outcome measure. Although we do not have a clear understanding of what the visual systems roll is in PLP relief, what is clear is that it should be incorporated into therapy for amputees!