Compound Exercises Show Metabolic Benefits
The gym is full of choices. But a new study suggests that when it comes to boosting your metabolism, not all exercises are created equal, pitting complex, multi-joint movements against their more focused, single-joint counterparts.
The debate isn’t new. For years, fitness enthusiasts have argued the merits of squats versus leg extensions. A 16-week randomized controlled trial published in the Journal of Applied Physiology now provides new, specific data. Researchers from the University of Toronto followed 120 previously sedentary adults, dividing them into two distinct groups. One group was assigned a routine built on compound exercises like deadlifts, bench presses, and overhead presses, while the second group’s workout consisted of isolation movements such as bicep curls and leg curls, with total workout volume and intensity carefully matched between them.
The metabolic differences were significant. The compound exercise group, according to the study’s data, saw their average resting metabolic rate (RMR) increase by 125 kcal per day. The isolation group’s RMR, in contrast, increased by only 45 kcal per day. The benefit extended well after the workout ended. So-called “afterburn,” or excess post-exercise oxygen consumption (EPOC), was substantially higher for those performing squats and deadlifts, with the effect lasting up to 24 hours and accounting for an additional 80-150 calories burned. The isolation group’s EPOC was minimal.
Dr. Anya Sharma, the study’s lead author and a kinesiologist at the University of Toronto, stated that the team observed more than just immediate caloric expenditure. “The data points to a persistent elevation in metabolic activity,” Dr. Sharma explained. She believes the body’s entire “energy-management ecosystem seems to be upregulated by these multi-joint movements.” This suggests the body has to work harder system-wide to recover from and adapt to the stress of moving a heavy load through a complex range of motion.
This isn’t just about aesthetics; it’s about reducing the risk factors for type 2 diabetes.
The benefits weren’t limited to energy burn. From an endocrine standpoint, the changes in insulin sensitivity were perhaps the most critical finding, according to co-author Dr. Ben Carter, an endocrinologist at Massachusetts General Hospital. The compound group experienced an 18% decrease in fasting insulin levels. The isolation group saw a much smaller 5% reduction. “The hormonal response to lifting a heavy barbell off the floor,” Dr. Carter noted, “is fundamentally different from curling a small dumbbell.” Better insulin sensitivity means the body is more efficient at managing blood sugar, a key marker for long-term metabolic health.
These hormonal and metabolic shifts translated directly to changes in body composition. The study, which used DEXA scans for precise measurement, found that participants in the compound group gained an average of 1.8 kg of lean mass while losing 2.2 kg of fat mass. The isolation group gained less than half the lean mass, at 0.9 kg, and lost only 0.7 kg of fat mass over the same 16-week period.
But the findings come with caveats. Dr. Julian Croft, a Stanford University researcher who was not involved in the study but reviewed its findings, points out that the participants’ sedentary history is a key variable. “Any activity would yield results,” Dr. Croft cautions, suggesting the real test is long-term adherence. The technical skill required for a heavy deadlift, he argues, presents a “higher barrier to entry and risk of injury” for a significant portion of the user base compared to a machine-based leg curl. This is a practical challenge for anyone looking to deploy these programs at scale.
Fitness technology companies will likely be watching this data closely. The compute power needed to accurately track the metabolic impact of a squat is far greater than for a bicep curl. Integrating this level of nuance into the algorithms that power wearables and fitness apps could improve the accuracy of calorie and activity tracking, but it would require a significant increase in data throughput from sensors that can monitor form and force, not just heart rate.
Dr. Sharma’s team is now seeking funding to integrate wearable sensor data into a follow-up study. The goal is to monitor movement quality, aiming to see if technique proficiency correlates with greater metabolic benefits.
