January 6, 2022 – In recent years, there has been a push to encourage doctors to be prescribe exercise as medicinethey tell their patients how often, how long and how hard to exercise to improve health.
A new Brigham Young University study suggests that doctors could take this initiative to the next level and prescribe exercise plans that lead to a specific health outcome; say lowering blood pressure or losing weight.
“The findings of this study and others suggest that we should be able to prescribe exercise more consistently and accurately, like medicine,” says lead study author Jayson Gifford, PhD, professor of exercise at BYU.
These exercise prescriptions would be tailored to patients based on a largely ignored measure of fitness called critical strength or maximal steady state—the fastest you can go while maintaining a pace you can sustain for long periods of time.
By building workouts around critical strength instead of the more commonly used VO2 max (maximum effort), we could more accurately predict health outcomes, just as we can with medicine, the researchers say. in Journal of Applied Physiology.
“We’ve known for centuries that exercise is part of the path to developing a healthy and long life,” says Jordan Metzl, MD, a sports medicine physician at the Hospital for Special Surgery in New York and author of Exercise regimen. “But it’s only been in the last 70 years that we’ve recognized the healing value of exercise.”
Metzl, who was not involved in the study, helped develop an annual seminar at Cornell Medical School that taught medical students ways to prescribe exercise beyond the cookie-cutter “30 minutes a day” recommendation. Yet doctors and other health professionals they often try to prescribe exercise to prevent or treat disease. AND a recent study from Oxford found that when doctors advise weight loss, it is often vague and difficult for patients to use.
“Exercise drug is one of the safest and most effective forms of preventive health,” says Metzl. “We need to get the medical community fully involved in prescribing exercise for their patients.”
This study suggests that a focus on critical strength could be the key to achieving this goal.
What the research found
In the study, 22 adults completed 8 weeks of either moderate-intensity training or high-intensity interval training, or HIIT. The intensity levels listed in both plans were based on VO2 max. So people in the study trained to a given percentage of their VO2 max.
Both groups saw improvements in endurance, but the results varied greatly from person to person. These mixed results may be explained by individual differences in critical strength.
“The improvement was much more correlated with the percentage of critical forces that individuals were working at than with the percentage of their VO2max, as exercise physiologists have thought for years,” says study leader Jessica Collins, a researcher at Brigham Young University.
Not only that, but several subjects who did not improve their VO2 max did see an increase in critical power and stamina.
“People tend to focus only on VO2 max,” says Gifford. “Many might see a lack of increase in VO2 max in some people and conclude that the training was ineffective. I personally believe that many potentially useful therapies have been ruled out due to the almost exclusive focus on VO2 max.
Critical strength has been shown to vary greatly from person to person, even between those with similar VO2 maxes.
“Let’s say you and Jessica had the same VO2 max,” explains Gifford. “If we were to keep you both at 70 percent. [your VO2 max]it can be above your maximum steady state, which would be really hard for you. And it can be below her maximum steady state that would make it easier for her.’
This means that you all stress your body differently, and this stress triggers improvements in fitness and endurance.
“Below critical force, metabolic stressors are well controlled and maintained at elevated but stable levels,” says Gifford. “Above a critical strength, metabolic stressors are produced so rapidly that they cannot be controlled and continue to build until they reach very high levels that cause failure.”
Knowing your critical strength means you can predict how these stressors will pile up and can tailor an exercise program to give you just the right “dose” of the stressor, Gifford says.
Such programs could be used for rehab patients recovering from heart attacks or lung disease, Gifford suggests. Or they could help older adults improve endurance and physical function, Collins notes.
But first, researchers need to confirm these results by programming workouts based on people’s critical strength and seeing how much the various measures improve.
How to find your critical power
Critical force is not new, but has been largely ignored by physiologists and health professionals because it is not easy to measure.
“People generally train outside of VO2 max or maximum heart rate, which is even less accurate,” says Gifford.
Finding the critical strength of people in the study involved several timed trials and calculating the relationship between speed/power and time, Gifford explains.
But for a rough measure of your critical strength, you can use an app that measures functional threshold strength (FTP), something Gifford refers to as the “Walmart version” of critical strength. “It’s not exactly the same, but it’s close,” he says. (Application Diet includes FTP as well as quite sophisticated power analysis.)
Or skip the technique and go with the feeling. If you’re below your critical strength, “it will be challenging, but you’ll feel in control,” says Gifford. Above your critical power, “your breath and heart rate will continue to rise until you fail within 2 to 15 minutes, depending on how high up you are.”
Still, you don’t need to know your critical strength to start exercising, notes Collins.
“The beauty of exercise is that it’s such a powerful medicine that you can see the benefits without fine-tuning your exercise that way,” he says. “I wouldn’t like it to become a hindrance to exercise. It’s important to do something.”
