Weight lifting: It's not just for young jocks anymore
In the elderly (including women) it excels at reducing the risk of falls, and excels at limiting the decline of cognitive abilities such as reasoning, recognizing, intuiting, and problem solving.
(20 seconds) A 64-year-old 100-pound Seattle, WA woman tests her mettle on a 184-pound barbell.
Falls
Since about 30% of people 65 and older fall at least once a year [Liu 2004], balance and stability is a big deal to them. About half the people in the over-65 group fall recurrently [Liu 2004] and because the falls often result in fracture or other disabilities, they can make the difference between being able to live on one's own or not.
Cognitive decline can be equally disabling. "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 a study in 2004 [Liu2004] found that weight lifting (ie, 'resistance training' or strength training) improves agility and balance more effectively than traditional training that is specific for agility and balance!
And a clinical trial [Liu-A 2010] in 2009 found that a once-per-week resistance training group scored 13% better on the Stroop test of cognition than a matched group given twice-weekly balance-and-tone-training!
Lifting weights improves physical agility?
Yes. A 2004 clinical trial of weight training (or, more technically, resistance training) and agility training for reducing risk of falls [Liu2004] involved 96 women with low bone mass aged 75-85. The exercises used for the resistance training included those shown below:
These are the exercises that resulted in lower risk of falls for women 75-85, and improved cognition for women 65-75 [Liu2004] [Liu-A 2010] |
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 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 risk of falls dropped by 57.3% for the resistance training group, compared to a drop of only 47.5% for the agility training group.
Lifting weights improves mental agility as well?
Yes again. Specifically, resistance training benefits the cognitive functions of selective attention and resolving conflicts between verbal and non-verbal cues. A clinical trial [Liu-A 2010] this year of cognitive effect from resistance training, versus that from balance and tone training (description below), involved 155 community-dwelling women aged 65-75. The exercises for the resistance training were essentially exactly the same as those depicted above. The balance and tone exercises trained for 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 resistance training group improved its performance on tests of selective attention and resolution of verbal-visual conflicts (like, "What color is this word: red ") by 12.6%, whereas the scores dropped by .5% in the balance and tone group.
Although it has been shown [Colcombe.2003] that cognitive function in the elderly improves most when both aerobic exercise and resistance training (anerobic) are involved, this study is not claiming that resistance training (alone) is better than aerobic exercise for cognitive function. Its purpose is only to show that resistance training has an independent contribution to cognition, rather than just 'potentiating' aerobic exercise. It also aims to quantify that independent contribution.
Evidence on the 'whole body' level for the benefits of weight-lifting
Sarcopenia, or loss of muscle tissue, is the analogue to osteoporosis, the loss of bone density. Both conditions increase risk of falls in the elderly and both may be helped more by resistance training than by any other type of exercise, since resistance training activates muscles more intensely than other exercises do, and excels at providing the weight-bearing activity that is essential to building bone density. [Liu 2009]
Resistance training also provides the satisfaction of being able to progress through small easily-quantifiable increments of challenge, such as increasing the weight of a dumbbell or barbell. One can progress without pressure at ones own speed.
And since resistance 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 resistance 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, resistance 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 resistance 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 resistance 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, resistance 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
2. In the resistance training and cognition study (see [Liu-A 2009] below), why did the once /week resistance 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 resistance 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
