The Lifelong Case for Muscle

The Grip Test on Oahu

Beginning in 1965, thousands of Japanese-American men living on Oahu passed through the Honolulu Heart Program. Among the measurements taken was a particularly uncomplicated one. The men, then between 45 and 68 years old, squeezed a hand dynamometer as hard as they could.

Twenty-five years later, 3,218 surviving members of an initially healthy group were examined again. Men who had belonged to the weakest third for grip strength in middle age were almost three times as likely as those in the strongest third to have a walking speed of 0.4 metres per second or slower. Difficulties with self-care were more than twice as common. The original measurement had taken seconds; the difference associated with it was still visible a quarter of a century later. [1]

Grip strength has subsequently appeared in much larger studies of mortality. The PURE study followed 139,691 adults in 17 countries. Each five-kilogram reduction in grip strength was associated with a 16 per cent higher hazard of death from any cause and a 17 per cent higher hazard of cardiovascular death. Within that cohort, grip strength predicted those outcomes more strongly than systolic blood pressure. It remained a marker, however, rather than a demonstrated cause: the study did not show that making somebody's grip stronger would itself extend life. [2]

The Jamar Dynamometer

A Jamar dynamometer looks more like something from a physiotherapy room than a piece of longevity technology. The handle moves little. A person simply closes a hand around it and applies force; the device supplies a number in kilograms.

Data from 12 British population studies show what happens to that number across a lifetime. Among 49,964 people, median grip strength in men reached about 51 kilograms between ages 29 and 39. Women reached a median peak of about 31 kilograms between 26 and 42. A period of relative stability was followed by decline from midlife. Using the study's stricter definition of weak grip, about 23 per cent of men and 27 per cent of women had reached that range by 80. [3]

Modern geriatric medicine has moved strength closer to the front of its assessment of muscle health. The European Working Group on Sarcopenia now treats low muscle strength as the first criterion for probable sarcopenia; low muscle quantity or quality is then used to confirm the diagnosis. Grip strength and the chair-stand test are among its recommended clinical tools. Calling strength a vital sign is still a proposal rather than routine medical convention, but the small dynamometer is measuring considerably more than the condition of the hand. [4]

The Fifth Decade

The Baltimore Longitudinal Study of Aging offers an unusually long view. Researchers measured grip strength and estimates of muscle mass in 847 healthy volunteers aged from 20 to 100. Strength rose into the thirties and its decline accelerated after 40. Age did not operate like a timer: during an average nine-year follow-up, 29 per cent of participants aged 40 to 59 experienced no decline in grip strength. [5]

Muscle also spends much of its working life away from anything that resembles lifting. Skeletal muscle accounts for roughly 80 per cent of insulin-stimulated glucose disposal. Glucose arriving in the circulation can be taken into muscle and stored as glycogen or used for energy, making the tissue an important participant in whole-body glucose regulation. Losing muscle therefore concerns metabolism as well as the ability to generate force. [6]

Quantity alone gives an incomplete picture. In the Health, Aging and Body Composition Study, 1,880 older adults were followed for three years. Leg strength fell roughly three times faster than leg lean mass. Some participants maintained or even gained lean mass without maintaining their strength. Muscle quality, neural control and the capacity to produce force were changing alongside the visible amount of tissue. [7]

Once or Twice a Week

In Vancouver, 155 women aged 65 to 75 were assigned to a year of exercise. Two groups performed resistance training, either once or twice each week. A comparison group attended balance and toning sessions twice weekly.

The primary cognitive test was the Stroop task, which requires a person to suppress an automatic response and resolve conflicting information. Performance improved by 12.6 per cent in the once-weekly resistance group and 10.9 per cent in the twice-weekly group; it declined slightly in the comparison group. The trial was testing a specific part of executive function, not whether weight training prevents dementia, and its participants were older women living independently in the community. [8]

The result placed a familiar gym activity in an unfamiliar setting. Resistance training had already been used to preserve force and physical function. Here the measured change appeared on a task of selective attention and conflict resolution. Research into exercise and cognitive ageing has continued to explore that relationship, with resistance exercise now sitting alongside aerobic activity in the study of later-life brain health.

One Hundred and Forty Calories

In 1960, about 48 per cent of jobs in American private industry required at least moderate physical activity. By 2008, that proportion had fallen to 20 per cent. Researchers who combined occupational data from the Bureau of Labor Statistics with estimates of the energy demands of different jobs calculated that daily work-related energy expenditure had fallen by about 140 calories for men and 124 for women over the period. [9]

The change was visible in the composition of work. Mining, construction and manufacturing were classified among the more physically demanding sectors in the study, while service occupations tended towards light or sedentary activity. The estimates did not even capture technological changes that reduced exertion inside a particular occupation.

For an increasing share of people, work stopped supplying much muscular loading at all. Physical effort that once arrived inside the working day increasingly had to be sought elsewhere. The office worker who trains after work is performing a curious modern separation: earning a living while largely still, then deliberately moving heavy objects for no productive purpose other than the effect on the body.

The Safety Margin

Current World Health Organization guidance asks adults to perform muscle-strengthening activity involving the major muscle groups on at least two days each week. For people over 65, it also recommends regular activity combining functional balance and strength. Resistance exercise has consequently acquired a place in public-health guidance that extends well beyond sport or physique. [10]

Stewardship is an old word for looking after something one expects to remain responsible for. Applied to physical strength, it can be quite literal. Getting out of a low chair requires a certain amount of force. Carrying something upstairs requires more. As the maximum force available declines, ordinary tasks consume a larger share of it.

The researchers who followed the men on Oahu used a similar idea. They described greater midlife strength as providing a “safety margin” above the threshold at which disability begins to appear. [11]

On Oahu, that margin was first recorded as a number in a man's hand. Twenty-five years later, it was visible in whether he could rise from a chair and cross a room