Good question. Here’s how I think about it.
Muscular strength is defined as the amount of force produced that is measured in a specific context. There a many different types of strength based on an activity’s velocity requirements, energy systems used, and other specifics of the task that are linked together by the common feature of muscular force production.
A growing number of large, prospective studies have found a strong, inverse relationship between physical strength and mortality (death) rates. Similarly, a number of studies show a strong correlation between muscular power and reduced risk of falling, maintenance of independence in older populations, and quality of life in general.
While it is clear that increasing levels of strength levels tend to improve health outcomes, we haven’t been able to quantify how strong is “strong enough” for health purposes. Much of the current literature uses standardized tests like isometric hand grip strength or knee extension strength to separate people into different groups, usually three tertiles, four quartiles, or five quintiles. We know that getting to the highest level is associated with lower mortality, but we two questions remain: 1. Does being at the top of the highest strength group (or higher) provide any incremental benefit over being at the bottom or middle?
2. Where is the cut-off for strength in order to “get into” the highest group? There’s not much available data to answer either question. A large study using data from the Aerobics Center Longitudinal Study that was collected at the Cooper Clinic in Dallas, TX between 1981 and 1989. This dataset included a muscular fitness assessment based on 1-min sit-up and 1-repetition maximal leg and bench press scores and a maximal graded treadmill test from 9762 men between 20–82 years of age. The researchers ranked subjects’ strength by a “muscle strength score”, which was the average of their “standardized” 1RM bench press and leg press values. The researchers standardized these values for an individual by taking the following formula:
(1RM value of individual - average value of all subjects in age group)/
standard deviation
The researchers followed these subjects for ~19 years to investigate all-cause mortality rates across low, moderate, and high muscular fitness groups.
The results of the study are described below:
- During follow up, 503 deaths occurred (5.7%)
- All-cause mortality was substantially lower in individuals in the highest tertile (third) of strength and cardiorespiratory fitness across all age groups
- The relationship between strength and mortality persisted even when correcting for baseline medical conditions, family history of heart disease, and baseline cardiorespiratory fitness The interesting part of this study was that the authors reported the average strength values for those in each tertile, which gives us some insight on “how strong is strong enough”. For example, the average leg press 1RM was 150kg (331lbs) or 1.9-times body weight in the upper third. By comparison, the average leg press 1RM was 125kg or 1.4-times body weight in the lower third. For bench press, the average 1RM was 84kg (184lbs) or 1.1-times body weight in the upper third and 62kg (136lbs) and 0.7-times body weight in the lower third.
Unfortunately, this data was only collected in men and we do not know the cut-offs for getting into the upper tertile or if there was a difference in mortality across individuals in the upper tertile. Still, this helps shed some light on how strong does someone need to get for health purposes.
These strength benchmarks are relatively low for those who have been lifting regularly for awhile, which suggests to me the “minimum strength” needed to avoid risk of disease secondary to weakness is likely low. I think developing additional strength is a good idea for sport or recreation, but I don’t know that it promotes greater health directly. Programs that produce improvements in strength, size, vo2max, etc. seem to benefit health more than similar volume/work programs that don’t. I think this is mostly due to the overlap between health and performance adaptations, but this is speculative.
-Jordan