October 2017

Strength drives survival: But benefits of training appear complex

In the moment: Rehabilitation

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By Keith Loria

Lower extremity strength appears to be a key variable in the relationship between mortality and compliance with national resistance exercise guidelines, according to research from the University of Mississippi in University, MS.

The study, which was epublished in September by the Journal of Physical Activity & Health, found greater knee extensor strength was associated with lower rates of cancer-specific mortality. Of the 2773 individuals aged 50 years and older who were analyzed, those in the highest quartile for knee extensor strength had a 50% lower risk of cancer-specific mortality after a mean of 9.7 years of follow-up, compared with those in the three lower quartiles.

Interestingly, however, the study also found self-reported participation in resistance training was not significantly associated with cancer-specific mortality. Individuals who said at baseline that they had participated in at least eight muscle-strengthening sessions in the previous 30 days (13.8% of the study population) were classified as meeting US Department of Health & Human Services guidelines recommending strengthening activities at least two days per week. Members of that group had an 8% lower risk of cancer-specific mortality than those who said they did strength training less frequently; the between-group difference, however, was not statistically significant.

“The actual outcome of strength appears to be more important than the behavioral engagement in resistance exercise,” said lead author Scott Dankel, MS, a graduate teaching assistant in the university’s Department of Health, Exercise Science, and Recreation Management.

This finding suggests monitoring knee extensor strength can help clinicians identify individuals at increased risk for cancer-specific mortality, and can also help determine if patients’ resistance training is actually resulting in improved strength.

“We feel that a large amount of the individual differences in muscle strength are simply genetic, but individuals can increase their strength to some extent via resistance exercise,” Dankel said. “We feel that the type of resistance exercise may be important to consider, as the exercise load or intensity used is directly propor­- tional to the improvements in strength.”

The findings also suggest the potential health benefits of resistance exercise other than increased strength (eg, improvements in blood pressure or cholesterol level) do not appear to affect cancer-specific mortality.

“Thus, we recommend that resistance exercises specifically targeting improvements in strength may be beneficial, since it is strength that is associated with cancer-specific mortality,” Dankel said.

Even though many clinicians do not have access to an isometric dynamometer to assess knee extension strength, Dankel said they could use an alternative assessment of lower body strength, such as a simple isotonic knee extension strength test that can be performed on a standard piece of gym equipment.

The lack of a statistically significant association between training and mortality in the
Mississippi study contrasts to an extent with a 2016 study, in which older adults who said they met national guidelines for strengthening exercises had lower all-cause mortality rates than those who didn’t (see “Get stronger, live longer: But few older adults meet US guidelines,” April 2016, page 13).

But the lead author of that study, Jennifer Kraschnewski, MD, MPH, associate professor of medicine and public health sciences at Penn State College of Medicine in Hershey, PA, said the new findings add to the argument that successful strength training is associated with decreased mortality.

Although clinical documentation of improved strength as a result of training in every individual would be ideal, Kraschnewski noted it may be impractical for busy practitioners, and that having the national guidelines be a goal for patients could still be valuable.

“The ability to have clinicians routinely measure lower extremity strength is unlikely to be successful, given other clinical demands,” Kraschnewski said. “Having clinicians encourage increased strength training activities is definitely an important step to help patients live healthier lives.”

Sources:

Dankel S, Loenneke JP, Loprinzi PD. Cancer-specific mortality relative to engagement in muscle strengthening activities and lower extremity strength. J Phys Act Health 2017 Sep 5:1-19. [Epub ahead of print]

Kraschnewski JL, Sciamanna CN, Poger JM, et al. Is strength training associated with mortality benefits? A 15 year cohort study of US older adults. Prev Med 2016;87:121-127.

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