Buzz
Heart rate zones are currently a major trend in fitness, with every smartwatch and tracker eager to show which 'zone' you're in during any activity—whether it's strength training or yoga. This might lead you to think that if your heart rate reaches zone 2 while lifting weights, you've effectively completed zone 2 training. Sadly, that's not the case.
Heart rate zones are designed for cardio
The concept of dividing heart rate into 'zones' stems from cardio training. In fact, monitoring heart rate for athletic purposes began with a Finnish ski team and later expanded to other sports. Your heart rate indicates how intensely you're working compared to past efforts, helping you decide whether to push harder or slow down. As Finnish triathlete Pauli Kiuri mentions in this Polar article, 'During a run, there comes a point where you feel you can't go on. But if your heart rate is only at 160 bpm, you have to trust that you can!' (Polar pioneered those early heart rate monitors.)
Heart rate training is particularly effective for endurance sports, as your heart rate increases with exertion. This relationship allows you to gauge your effort level by monitoring your heart rate: the higher the number, the more intense your workout. Essentially, your heart rate serves as a reliable indicator of your physical effort.
However, this correlation between heart rate and effort doesn't apply to all forms of exercise. For instance, your heart rate during yoga doesn't reflect how deeply you're stretching, nor does it indicate whether you're lifting light or heavy weights during strength training. This is why your heart rate during strength training is irrelevant.
Heart rate zones provide insight into your overall physical activity, not just your heart's performance
When used correctly, heart rate is a proxy metric. We don't monitor heart rate for its own sake; we track it because it offers valuable information about something else—specifically, the intensity of cardiovascular exercise.
Zone 2 cardio offers several benefits, including low-fatigue calorie burning, enhanced mitochondrial and capillary density, and improved VO2max, among others. These advantages stem from the fact that your entire body is engaged in the exercise.
Our muscles undergo repeated contractions, demanding more energy from our mitochondria to sustain the effort. This increased energy requirement enhances our cells' insulin sensitivity, allowing them to absorb blood sugar more efficiently. To support this process, our bodies develop additional capillaries to deliver nutrients and oxygen to muscle cells while removing metabolic waste.
This holistic process is the essence of 'zone 2' training. Simply raising your heart rate without engaging in these physiological changes won't yield the benefits of zone 2 adaptations.
This is why a stressful 30-minute work meeting isn't equivalent to a jog, and watching a scary movie doesn't compare to a HIIT session. Similarly, a sauna isn't a substitute for exercise. (While saunas may slightly improve blood vessel health, they don't provide the full range of benefits.) In reality, zone 2 cardio shares more similarities with zone 3 or even zone 5 cardio than it does with 'zone 2' strength training.
What zone is ideal for strength training?
It's a trick question! Heart rate zones are irrelevant for strength training. There are numerous ways to measure your effort during weightlifting, none of which involve a heart rate monitor. Here are some common methods to assess your intensity:
Comparing the weight on the bar to your personal best: for instance, you might perform squats at 80% of your maximum capacity.
The number of repetitions at a specific weight: completing five reps at 80% is more challenging than a single rep at the same percentage.
The speed at which you perform each rep: increased difficulty results in slower movement; specialized devices can even measure this, often referred to as 'bar speed.'
How many additional reps you could have managed: if you had three reps left 'in the tank,' the set was easier compared to pushing yourself to your absolute limit.
The level of soreness, fatigue, or 'pump' in a muscle: in certain training styles, this helps determine how much work a muscle group has undergone during the session.
Certain factors, such as feeling out of breath after a set or having an elevated heart rate during or post-exercise, do not indicate how effectively you're building strength.
When lifting weights, your heart rate might spike, your breathing may become labored, and rest periods could lengthen—if your cardiovascular fitness is lacking. This suggests you might benefit from incorporating actual cardio (zone 2 or otherwise) to improve fitness and reduce recovery time between sets. However, cardio fitness is secondary here; it's not the primary focus of strength training, nor is it a reliable measure of your effort.
To put it differently: whether you complete five sets of five squats at 80% of your max with three-minute rests and ease, or eight-minute rests and a high heart rate, the strength gains remain the same.
But what heart rate zones are typical for strength training?
During a strength training session, your heart rate will likely fluctuate significantly. While resting, it may drop to zone 1 or 2, but during intense sets, it can surge into zone 3 or beyond.
Higher rep sets, such as 10 reps, often result in a more elevated heart rate compared to lower rep sets like three reps. However, the specific heart rate zone you're in during these moments is irrelevant.
When reviewing your heart rate chart post-workout, the key detail to note is the presence of sharp peaks and valleys. A relatively flat chart suggests you're not resting adequately. For example, compare my recent jog (at the upper end of zone 2/lower zone 3) with a strength session involving snatches, deadlifts, and squats. Notice the longer rest periods and higher spikes, especially during heavy six-rep squats toward the end.
If heart rate zones aren't relevant, why does my app still display them for strength training?
The simple explanation is: because it's possible, not because it's necessary.
Initially, endurance athletes embraced heart rate training as an alternative to pacing by time or intuition. They recognized it as a way to gauge overall effort during activities like running or skiing.
Today, with every smartwatch tracking heart rate, the situation has changed. Heart rate zones appear on your results because they're easy for your watch to measure and for your app to compute. Additionally, the companies behind these products aim to impress you with visually appealing charts after each session.
Heart rate zone charts add a sense of significance to your workout, acting like a small reward sticker to encourage consistency (and, from the company's perspective, continued product use). While it's fine to enjoy these charts, focus on the metrics that truly matter—which, for strength training, excludes your heart rate.
