“Strength training and cardio workouts can have different short- and long-term effects on your blood glucose (sugar),” says Sheri Colberg, PhD, Professor Emerita, Exercise Science, Old Dominion University, founder of Diabetes Motion, and one of the world’s leading experts on diabetes and exercise.
Diabetes Blood Sugar Control: Cardio vs. Strength Training
“In general, strength training causes a greater release of glucose-raising hormones like glucagon and adrenaline, and your blood glucose is less likely to drop and may even go up when you do intense strength workouts,” says Dr. Colberg.
“Cardio workouts that last for 30 to 60 minutes are usually done at a more moderate workload and lower blood glucose more than intense ones or strength training,” continues Dr. Colberg.
Intensity a Key Factor
HIIT cardio involves, for instance, sprinting as fast as you can across a parking lot (very intense!) and then walking slowly around for several minutes to recover – alternating this way for 20 minutes total.
You’ve done actual work for maybe three minutes total, but high intensity interval training (three minutes’ total work, 17 minutes recovery walking) is far more intense than a continuous 5 mph jog around that parking lot for even 40 minutes.
So as far as lowering blood sugar, “It depends a lot on the intensity of the workouts,” says Dr. Colberg.
Light effort can also mean a weight training session in which you stop at 12 repetitions at light resistance, but feel you could have done another 12.
The session is even more docile when most of the exercises isolate small muscles, such as with the inner and outer thigh machines, biceps curls, triceps kickbacks and dumbbell side lifts.
“All intense exercise of any type has the potential to temporarily raise blood glucose instead of lowering it,” says Dr. Colberg.
Intense strength training would be 1) a focus on big multi-joint moves like the bench press, leg press, back squat, deadlift and overhead barbell press, 2) an eight to 12 rep max in which rep 13 is impossible due to so-called muscle failure, and 3) short rest periods.
“As far as the longer term effects go, your blood glucose will tend to drop more after resistance training if you use up lots of stored carbs from muscle (glycogen), and you may drop overnight, whereas cardio workouts may have less of an impact on your blood glucose later on.
“Many other factors impact how your blood glucose responds to any given workout, though, including exercise type, the time of day, when you last ate, what your medication regimen is and environmental factors, to name just a few.”
Study Shows Better Blood Sugar Control when Strength Training Precedes Cardio
Canadian researchers showed that if weights and cardio are done in the same session, diabetics gain better blood sugar control when they lift weights first.
However, the study, led by endocrinologist Dr. Ronald Sigal, focused only on type 1 diabetes.
• 12 type 1 diabetics, already fit from cardio and weight training, participated.
• They worked out in a lab setting twice with at least five days apart.
• One session was 45 minutes of treadmill cardio followed by 45 minutes of strength training.
• The other session was in reverse order.
• Each session began at 5 pm.
• Blood sugar was measured before, during and after the sessions.
The target glucose for type 1 diabetics is 4 to 10 mmol/L.
If the participants’ glucose dropped below 4.5 mmol/L, they were instructed to stop exercising and eat.
Doing cardio before weights caused blood sugar to drop closer to that threshold and remain lower during the remainder of the workout than when subjects did strength training first and cardio after.
Needless to say, when strength training was done before cardio, there was less of a drop in blood sugar in the hours following the session. Post-workout glucose drops also tended to last shorter.
This study shows what previous research reveals: Cardio causes a faster drop in blood sugar than does strength training.
Bear in mind that this was a small study and that, as Dr. Colberg mentioned, other factors influence glucose level.
The Canadian team acknowledges that other factors, that were not accounted for, could have influenced glucose readings.
This includes what the participants ate prior to the lab sessions.
The report, which appears in Diabetes Care, also points out that the results may not apply to type 2 diabetics, unfit diabetics or older diabetics (mean age of study subjects was 32).
So don’t take these study results as the gospel. But it won’t hurt to do strength training before cardio if you have no choice but to combine both in the same session.
However, the diabetic (as well as general population) is served best when strength training and cardio are done on separate days.
This will also be better for blood sugar control.