Strength training: It's not just for young jocks anymore

In the elderly, both women and men, strength training excels at reducing the risk of falls and at limiting the decline of mental functions such as reasoning, recognizing, intuiting, and problem solving.


A 64-year-old 100-pound Seattle, WA woman tests her mettle on a 184-pound barbell (20 sec. video). The ability to do this is the result of persistence, not pain. Pushing oneself to a satisfying 'burn' is desirable, but otherwise No pain no gain is a myth.

Falls and forgetfulness

Brain-to-muscle talk goes in both directions.  The brain sends messages to the muscles to contract, and gets messages back. Spinal cord. Muscle fiber. Approximately 30% of people 65 or older fall at least once a year [Liu 2004], so balance and stability are a big deal to them. Because half of those over 65 fall repeatedly [Liu 2004] over the course of aging, and because those falls often result in fractures or other problems, falling can make the difference between being able to live on one's own or being limited and dependent.
A decline in mental sharpness can be equally disabling, as well as financially crippling: "In 2000, Alzheimer's disease and other types of dementias were the third most expensive health care condition in the USA, preceded only by heart disease and cancer".[Liu 2009]


Consider then, that the same study as above [Liu2004] found that strength training (a.k.a. weight lifting or 'resistance training') improves agility and balance more effectively than traditional agility and balance training!

Strength training improves physical agility?

Yes. A 2004 clinical trial compared strength training to agility training for their ability to reduce the risk of falls [Liu2004] and involved 96 women age 75-85 who had low bone mass. The exercises used for the strength training included those shown below:

These are the exercises that resulted in lower risk of falls for women 75-85; they also improved mental function for women 65-75 [Liu2004] [Liu-A 2010]

bicep.curl
This strengthens the biceps muscles in the front of the upper arm

This strengthens the triceps muscles in the back of the upper arm

This strengthens the muscles in the upper back

This strengthens the quadriceps and hamstring muscles in the upper leg

This strengthens the hamstring muscles in the back of the upper leg

This strengthens the calf muscles in the back of the lower leg

This strengthens the muscles in the back

This strengthens the quadriceps and hamstring muscles in the upper leg

The agility-training exercises included obstacle courses, dance movements, relay races and ball games. At the end of 6 months of training via twice-weekly classes, the agility in both groups improved, but agility improved more in those who did the strength training. That is, the risk of falls dropped by 57.3% for the strength-training group, compared to a drop of 47.5% for the agility-training group.

Strength training improves mental agility as well?

Yes again. And a clinical trial clinical trial [Liu-A 2010] in 2009 found that a once-per-week strength training group scored 13% better on the Stroop test of cognition than a matched group given twice-weekly balance-and-tone-training!
Specifically, strength training benefits the cognitive functions of selective attention and resolving conflicts between verbal and non-verbal cues. A clinical trial [Liu-A 2010] of improvement in brain function from strength training compared to balance and tone training involved 155 community-dwelling women aged 65-75. The exercises for the strength training were essentially the same as those depicted above. The balance and tone exercises emphasized range of motion, balance, and core strength. Relaxation techniques were included as well.

At the end of the 12 months of training, the once-per-week strength training group improved its performance on tests of selective attention and resolution of verbal-visual conflicts by 12.6%, whereas the scores dropped by .5% in the balance and tone group. An example of a verbal-visual conflict might be "What color is this word: red ".

Although it has been shown [Colcombe.2003] that cognitive function in the elderly improves most when both aerobic exercise and strength training (anerobic) are involved, this study is not claiming that strength training alone is better than aerobic exercise for cognitive function. Its purpose is to show that strength training has an independent contribution to improving mental function, rather than just increasing the benefits of aerobic exercise.

Evidence on the 'whole body' level for the benefits of weight-lifting

Sarcopenia -- the loss of muscle tissue -- is analogous to osteoporosis, the loss of bone density. Both conditions increase the risk of falls in the elderly and both osteoporosis and sarcopenia may be helped more by strength training than by other types of exercise. Strength training activates muscles more than other exercises do, and also excels at providing the weight-bearing activity that is essential for building bone density. [Liu 2009]

Strength training also provides the satisfaction of being able to progress at ones own speed. Easily-quantifiable increments of challenge, such as increasing the weight of a dumbbell or barbell, allow a participant to tailor exercises her or his own specifications.

And since strength training (as well as agility training) needs to be pursued long term to have lasting benefit, it's nice that it can be pursued enjoyably, with visible progress on a regular basis. It is much more difficult to experience the same sorts of milestones through agility exercises.



Clues on the molecular level, to how strength training may be increasing cognition and lowering the risk of falls

Two molecules that appear to have a role in this are one, a beneficial hormone (Insulin-like Growth Factor IGF-1) and two, a detrimental amino acid homocysteine. In humans, strength training increases the good hormone and decreases the bad amino acid. [Liu 2009]

IGF-1 promotes the growth, survival, and specialization of the nerve cells [Cotman 2002], probably by enhancing the transport of amino acids across cell membranes for protein synthesis [Spirduso 1982]. Homocysteine has not only been associated with impaired cognitive performance and Alzheimer's disease, but with increased bone fractures in the elderly as well.[Liu 2009]


The 'talk' between the nervous system and muscular system goes in both directions

A "nutritive" effect of a nerve on the muscle that it stimulates to contract [Guth1968], and of the muscle reciprocally on the nerve as an indirect result of having contracted, is a 'trophic effect'.[Eccles 1973] The point of contact between the nerve and muscle is the synapse or synaptic terminal and when nutritive activity is flowing from nerve to muscle, the muscle is the 'postsynaptic cell'. Thus,

"...muscle properties and integrity may influence the effectiveness of synaptic terminals. Postsynaptic cells may transfer chemical(s) to the presynaptic terminals... ...This type of mechanism could account for the maintenance of healthy synaptic terminals throughout life. The nerve cell usage hypothesis, suggesting that frequent firing of action potentials postpones cell aging,.. could involve a trophic exchange.... Although Eccles [Eccles 1973] traced the trophic effect of muscular contraction into the central nervous system only so far as its innervating neuron and immediate central connections, the trophic exchange of muscular activity could include to some degree the entire multilevel neuronal network contributing to the movement."[Spirduso 1982]

It's widely known that exercise in general improves brain function [Colcombe.2003] and since all exercise involves the contraction of muscles, there may be a lot more than just increased blood flow to the brain that muscle contraction 'gives' to the brain.

'The entire multilevel neuronal network' (neuron connecting to neuron connecting to neuron) includes: the cerebellum in the brain, which influences balance through its control of muscular coordination; the vestibular nervous system (the semi-circular canals), which affects balance directly; and the frontal cortex and limbic system, which are key players in all cognitive function.

And since strength training involves the most intense muscle contractions it stands to reason that it may provide more reciprocal benefit for the brain than exercises of less intense contraction, and seemingly do more than agility training itself to hone control over the muscles needed (for instance) for catching oneself from a fall:

"...There can be little question that the amount and type of work that a muscle does will also affect its biochemical composition. Heavy weight lifting exercise results in a relative increase in myfibrillar protein..." and "...The muscle cell is capable of a wide range of physiological adaptations; it exhibits different metabolic responses to hormones, type of exercise, and type of disuse."[Guth 1968]


The 'motor unit' is where the talk happens in one direction and may be happening in both

A motor unit is a neuron and the group of muscle fibers innervated by it. One reason that brain-communication-to-muscle tasks are more problematic for the elderly is because there are fewer nerves communicating with fewer muscles as we age: "In the normal adult, motor unit loss with aging is dramatic [and] it's estimated that less than half of the motor units present in youth remain in the aged individual." [Spirduso 1982] Fortunately, this loss is reversible [Spirduso 1982] and it may be that strength training is the exercise which reverses the loss most efficiently.

If falls are at least partly due to the lack of strength to stop a fall once the momentum of the fall has begun, then physical strength would make a difference in whether a fracture results from the momentary loss of balance. In other words, the stronger the leg muscles are that you stand on, the more easily your legs can stabilize the weight above them.

A study published in 2007 found that even after a (healed) hip fracture, there is benefit and safety in strength training when "working at high intensities in order to optimize gains in strength and physical function." [Host.2007] So at least part of the means by which agility and balance training improve agility and balance may be due to whatever muscle strengthening results from it.

In answer to the question of how a type of exercise that involves little or no balancing could help ones ability to balance, one source asserts that

"...some evidence exists that a moderate level of physical fitness modulates an organism's neuromotor capacity to perform psychomotor [brain-communication-to-muscle] tasks even when the response requires very little physical effort and is totally different from the physical activity used to develop physical fitness." [Spirduso 1982]

In other words, exercises un-related to balance-specific training still stimulate the nervous system. As the nervous sytem becomes more efficient (from a larger number of motor neurons working together), more muscle fibers work 'in concert' to produce smoother, greater-controlled movements. This in turn improves balance and stability.

A take-home message

Even without the benefits on all these levels, strength training would be valuable for living fully when old. You can't get the lids off of difficult jars without a fair amount of strength. The same is true for carrying buckets of dirt in the garden, carrying furniture in the house, shoveling dirt or snow, getting boxes on and off of overhead shelves, or defending oneself when in danger.


Some unanswered questions

1. Only one gender was used in the clinical trial for testing effect on cognition because "cognitive response to exercise differs between the sexes." [Liu 2010] -- what's that about? How/why does it differ?

2. In the strength training and cognition study (see [Liu-A 2009] below), why did the once /week strength training subjects do better cognitively than the twice /week subjects?

3. How reproducible are these cognitive results in significantly younger or middle-aged people? Exercise in general has been shown to improve cognitive performance in all ages [Liu2009]; but does strength training, compared to other types of exercise, have this beneficial effect before age 65?

4. For IGF-1 and homocysteine: What are the intermediate steps in the metabolic pathway that starts with the triggering of an intense muscular contraction and ends with higher IGF-1 and lower homocysteine?

A bonus tip: How not to exercise



References

Thanks to Jonathan Blodgett BS, CSCS, community college fitness instructor and personal trainer for help on the fitness science in this article.

[Colcombe.2003] Colcombe S, Kramer AF. Fitness effects on the cognitive function of older adults: a meta-analytic study. Psychol Sci. 2003;14(2):125-130. Abstract

[Cotman 2002] Cotman CW, Berchtold NC. Exercise: a behavioral intervention to enhance brain health and plasticity. Trends Neurosci 2002;25:295–301.

[Eccles 1973] Eccles, JC. Trophic influences in the mammalian central nervous system. In Development and Aging in the Nervous System, ed. M. Rockstein. New York: Academic Press 1973

[Guth 1968] "Trophic" influences of nerve on muscle. Guth L. Physiol Rev. 1968 Oct; 48(4):645-87.

[Host 2007] Training-Induced Strength and Functional Adaptations After Hip Fracture, Helen H Host, David R Sinacore, Kathryn L Bohnert, Karen Steger-May, Marybeth Brown and Ellen F Binder PHYS THER Vol. 87, No. 3, March 2007, pp. 292-303. Abstract

[Liu-A 2004] Resistance and agility training reduce fall risk in women aged 75 to 85 with low bone mass: a 6-month randomized, controlled trial. Liu-Ambrose T, Khan KM, Eng JJ, Janssen PA, Lord SR, McKay HA. J Am Geriatr Soc. 2004 May;52(5):657-65. Abstract

[Liu-A 2009] Exercise and cognition in older adults: is there a role for resistance training programmes?Liu-Ambrose T, Donaldson MG. Br J Sports Med. 2009 Jan;43(1):25-7. Abstract

[Liu-A 2010] Resistance training and executive functions: a 12-month randomized controlled trial. Liu-Ambrose T, Nagamatsu LS, Graf P, Beattie BL, Ashe MC, Handy TC. Arch Intern Med. 2010 Jan 25;170(2):170-8. Abstract

[Spirduso 1982] Spirduso W. Physical fitness in relation to motor aging. In: Mortimer J, Pirozzolo F., Maletta G., eds. The Aging Motor System. New York: Praeger, 1982, pp 120–151.

 
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