Same workout. Different bodies. Very different results.

Last week, we decided to put our bodies to the test.

Same workouts. Same rest. Same environment.

The only difference?

Jacob is 6’2” and weighs 215 pounds. Benji is 5’10” and weighs about 140 pounds after dinner.

We ran. We lifted. We swam. And we tracked everything — especially our heart rates.

We wanted to find out:

• How does the same workout affect two very different bodies?

• Would our heart rates respond the same?

• Who would recover faster?

• Would the effort feel equal?

On one hand, it’s pretty common sense that someone carrying more body mass is going to find the same workout harder, and their heart will have to work harder. 

But why is that, actually?

Here’s the science: 

All else being equal, a heavier person will typically have a higher oxygen demand during exercise, especially in exercises that require weight-bearing, like running. That extra mass requires more energy to move, and the cardiovascular system has to work harder to deliver enough oxygen to the muscles doing the work. One of the body’s key tools to meet this demand is ramping up heart rate.

But heart rate isn’t just about weight. It’s influenced by a few key factors: the total cardiac output your body needs (how much blood it has to circulate), your fitness level (the more trained you are, the more efficiently your heart works), and your mechanical efficiency (like stride length or how efficiently your muscles contract). So if Jacob were significantly more trained than Benji, or had a more efficient stride, his heart rate during exercise might actually be lower — even with 80 more pounds on his frame. But assuming similar levels of fitness and efficiency, a heavier athlete like Jacob will generally show a higher heart rate when doing the same bodyweight workout as someone lighter.

There’s also a fairly linear relationship between body weight and oxygen cost. The VO₂ requirement of a task like running increases proportionally with mass — roughly 1 milliliter of oxygen per kilogram per minute for every kilometer per hour of speed. That means someone who weighs 220 pounds (100 kg) is consuming around 43% more oxygen than someone who weighs 140 pounds (63.5 kg) while doing the same workout. Again, that increased demand is often reflected in heart rate.

If you want a simple rule of thumb: each pound of body weight adds about 0.8–1% to the energy cost of running. That doesn’t mean your heart rate will go up by the exact same percentage — but it’s still a useful guideline. More weight generally means more oxygen needed, which typically results in a higher heart rate — unless the individual is especially well-trained and adapted.

It’s also worth noting that different types of heart rate tell different stories. Your max heart rate doesn’t change based on your weight — it’s mostly tied to age (around 220 minus your age is the rough estimate). Your resting heart rate tends to be lower the more aerobically fit you are, no matter your size. But your working heart rate — what your heart does during exercise — tends to be higher in heavier or less-fit individuals, especially when performing the same absolute workload.

We decided that all of this made sense in theory, but we wanted to see what the actual difference would be if we spent a few hours working out together and comparing our data. 

Here’s what we found.

1. Our Baseline Data

For this to be a fair test, we should take a look at how well recovered each of us was and how we’d slept. Somehow, without meaning to, we both had a pretty bad night of sleep, so we ended up with a similar amount of rest.

However, according to Whoop, Benji was more recovered. 

Sleep pre-workout day:

(via Whoop)

(Benji via Garmin: 5 h 58, 47 resting heart rate, 74/100)

We started with a fairly gentle 5k. The first interesting difference is that our different devices captured the distances quite differently—Benji’s Garmin told us we’d done just shy of 3 miles, and Jacob’s phone clocked in at 3.12 miles. 

That aside, there was a 15 bpm difference in heart rate, with Jacob’s body working harder to keep the pace. This bump is actually about in line with what you would expect based on the extra body mass, so maybe it’s a sign that Jacob isn’t actually incredibly far off from Benji in fitness, once you factor in the greater weight. 

(via Whoop)

(Whoop's "Activity Strain" is a proprietary metric designed to quantify the cardiovascular load your body experiences during a specific activity. It gives you a number on a scale from 0 to 21, with higher numbers representing more intense or prolonged cardiovascular effort.)

(Benji via Garmin, Jacob via Strava)

2. Badminton

We played about an hour of badminton, and logged the following data…

(via Whoop)

(Benji via Garmin: 116 bpm, 52:45, 348 calories)

3. Tennis:

We played some tennis right after, and logged the following data…

(Benji via Garmin: 114 bpm, 55:59, 334 calories)

4. Gym:

We spent about 45 minutes lifting and logged the following data. Interestingly, this segment shows that heart rate can’t always be trusted to tell the full story, because both of us remember Jacob struggling more with this workout (i.e. taking more breaks during sets). In fact, it might be because he was taking more breaks within sets that his heart rate was lower. Or perhaps in this workout, Jacob’s bodyweight ended up being a strength advantage, leading to a different comparison. 

(via Whoop)

(Benji via Garmin: 117 bpm, 42:26, 288 calories)

5. Swimming

We ended the day with about 800m of swimming. 

(via Whoop)

(Benji via Garmin: 121 bpm, 22:59, 2:52/100m, 200 calories, 800m swam)

6. End of day 

(via Whoop)

(Jacob walked about a mile and a half in the morning, which explains the step discrepancy!) 

7. Recovery

How quickly did both of us recover?

Here’s our Whoop data for the next couple of days:

Takeaways:

From heart rate patterns to calorie expenditure and strain scores, it’s clear that Jacob’s higher weight demanded more effort to complete the same tasks. This supports the well-established principle that heavier individuals, even if similarly fit, generally experience greater cardiovascular and metabolic loads during weight-bearing exercises like running or court sports.

One of the most consistent findings across all activities was Jacob’s elevated heart rate and energy expenditure. Whether we were running, playing badminton, or swimming, his heart had to work harder, and his body burned more calories. 

However, it’s worth noting that these physiological demands didn’t necessarily mean he is less fit—rather, they reflect the greater workload required to perform the same activity with a bigger body.

Not all of our data was perfectly aligned with our expectations, though. For instance, during the gym session, Jacob actually showed a lower average heart rate despite feeling like he struggled more. This disconnect points to the limitations of using heart rate alone to gauge effort in strength-based workouts, where factors like rest time and movement type can dramatically influence cardiovascular response. A reminder that no single metric tells the full story of physical exertion or performance.

Interestingly, both of us recovered well in the days that followed, showing that our bodies adapted relatively efficiently to the physical strain. Although Jacob experienced more exertion during the workouts, his recovery data wasn’t crazy different, which could speak to an underlying fitness level. 

(Although he did physically ache for DAYS!) 

The key takeaway from all of this? The same workout will never truly be “equal” between two people with different physiologies. Body size, composition, efficiency, and fitness level all shape how a workout feels and what it demands. 

That’s not a flaw—it’s just reality. And understanding these individual differences can help us train smarter, compare more fairly, and focus less on matching numbers and more on matching effort and intention.

We hope you enjoyed reading! 

Until next time, 

Benji and Jacob.

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