“Is My Heart Rate Too High?” Understanding Exercise Effort During Cardiac Rehabilitation

Starting cardiac rehabilitation after a heart event can feel daunting. Many people tell us their biggest concern isn’t whether they can exercise — it’s whether they might overdo it.

“How hard is too hard?”

“What if my heart rate goes too high?”

These concerns are completely understandable. After a heart attack, heart surgery, or cardiac procedure, it’s common to feel unsure about what your heart can safely tolerate.

At Body Fit Physiotherapy, we place a strong emphasis on helping people exercise with confidence rather than fear. One of the most effective ways we do this is by using the Modified Borg Rating of Perceived Exertion (RPE) alongside heart rate monitoring — a combination supported by cardiac rehabilitation guidelines and everyday clinical practice in Australia.

This article explains how the Modified Borg Scale works, how it relates to heart rate, and why we find this approach so helpful for people recovering from a cardiac event.

Why Exercise Intensity Matters After a Heart Event

Exercise is a key part of recovery after a cardiac event. Research consistently shows that appropriately prescribed exercise improves cardiovascular fitness, functional capacity, confidence, and quality of life, while reducing the risk of future cardiac events.

The important part is how that exercise is guided.

Too little challenge may limit progress.

Too much, too soon can have negative effects or increase anxiety.

This is why cardiac rehabilitation focuses on safe, individualised exercise intensity, rather than pushing limits or chasing numbers.

How We Measure Exercise Effort in Cardiac Rehabilitation

In cardiac rehab, effort is usually monitored using:

• Heart rate

• Perceived exertion (how hard the exercise feels)

At Body Fit Physiotherapy, we primarily use the Modified Borg Scale (0–10) because it is:

• Simple and intuitive

• Easy to remember

• Well validated in cardiac populations

• More practical for long-term self-management

What Is the Modified Borg Scale?

The Modified Borg Scale is a 0–10 rating system that helps you describe how hard an activity feels at that moment.

Rather than focusing on technology alone, it encourages you to listen to your body — breathing, muscle fatigue, and overall effort.

MODIFIED BORG SCALE

What Effort Level Is Usually Targeted in Cardiac Rehab?

For most people in cardiac rehabilitation, exercise is typically prescribed at:

Modified Borg 3–4 (Moderate Intensity)

This usually feels like:

• Breathing faster but still able to talk in short sentences

• Feeling warm and worked, but not overwhelmed

• Something you could continue for a reasonable period

As fitness and confidence improve — and where medically appropriate — some people may gradually progress to Borg 4–5, always with guidance and monitoring.

How Does This Relate to Heart Rate?

Although the Modified Borg Scale is subjective, it generally corresponds to heart rate intensity zones.

As a broad guide (not a strict rule):

• Borg 3–4 often aligns with ~50–70% of maximum heart rate

• Borg 5–6 may align with ~70–80% of maximum heart rate

However, this relationship can vary significantly from person to person.

Why Heart Rate Alone Isn’t Enough

Heart rate monitoring is useful, but it doesn’t tell the whole story — especially in cardiac rehabilitation.

Several common factors can affect heart rate response:

Medications

Many people take medications (such as beta blockers) that intentionally reduce heart rate or limit how much it rises during exercise. This makes standard heart rate formulas less reliable.

Individual Fitness History

Someone who was physically active before their cardiac event may tolerate higher heart rates comfortably compared to someone new to exercise — even at the same perceived effort.

Daily Variation

Sleep, hydration, stress, temperature, and recovery all influence heart rate.

Anxiety

It’s common for heart rate to rise due to nervousness alone, particularly early in rehab.

Because of this, heart rate numbers without context can sometimes increase worry rather than provide reassurance.

Why We Combine Modified Borg + Heart Rate at Body Fit

At Body Fit Physiotherapy, we don’t rely on rigid formulas or single numbers.

Instead, we combine:

• Modified Borg RPE (how the exercise feels to you)

• Heart rate monitoring

• Clinical observation

• Your symptoms, confidence, and goals

This approach allows us to:

• Adjust exercise intensity safely and in real time

• Account for medications and recovery stage

• Teach you how to self-monitor beyond the clinic

• Build trust in your body again

Many people find that, over time, they rely more on how exercise feels — an important step towards independence and long-term heart health.

What Exercise Should Feel Like During Cardiac Rehab

Most sessions should feel:

• Challenging but controlled

• Purposeful, not frightening

• Something you recover from well

  
  

Mild breathlessness, warmth, and muscle fatigue are normal. Exercise should generally leave you feeling better afterwards, not worse.

If something doesn’t feel right, that’s information — not failure — and it’s always worth discussing with your rehab team.

When to Pause and Seek Advice

While cardiac rehabilitation is considered very safe when appropriately supervised, you should let your physiotherapist or medical team know if you experience:

• New or worsening chest discomfort

• Unusual or persistent shortness of breath

• Dizziness or light-headedness

• Palpitations

• Ongoing anxiety that limits your confidence to exercise

These symptoms don’t automatically mean something is wrong, but they do deserve careful review and reassurance.

Confidence Is Part of Recovery

Cardiac rehabilitation isn’t just about improving fitness — it’s about rebuilding trust in your body.

Understanding effort, learning what is safe, and having guidance as you progress allows you to return to daily life with less fear and more confidence.

That confidence is just as important as the physical gains.

How Physiotherapy Supports Cardiac Rehabilitation

As physiotherapists with a special interest in cardiac rehabilitation, we focus on:

• Individualised exercise prescription

• Clear education around effort and safety

• Teaching you how to monitor intensity confidently

• Supporting both physical and emotional recovery

• Helping you transition to long-term, independent exercise

Your recovery is not a race — and it doesn’t need to follow someone else’s timeline.

Key Takeaways

• Feeling unsure about heart rate and exercise is common after a cardiac event

• The Modified Borg Scale (0–10) is a safe, simple way to guide effort

• Heart rate targets vary due to medications and individual factors

• Combining Borg with heart rate monitoring provides the clearest guidance

• Confidence grows with understanding and gradual progression

If You’d Like Support

If you’re recovering from a cardiac event and would like help understanding how hard to exercise — or how to feel confident being active again — a physiotherapist trained in cardiac rehabilitation can help guide the next steps.

At Body Fit Physiotherapy, we take the time to listen, understand your concerns, and support your recovery in a way that feels safe and achievable.

📍 Body Fit Physiotherapy – North Adelaide

🌐 bodyfit.life

📞 8267 6432

We’re always happy to help if you’d like support.