Beta Blocker Side Effects During Workouts: Fatigue, Low Heart Rate, and When to Call Your Doctor

Beta blockers are medicines that reduce the effects of stress hormones on the heart. In simple terms, they slow the heartbeat and reduce how forcefully the heart contracts, which can be helpful for conditions such as high blood pressure, abnormal heart rhythms, angina, and after a heart attack. ^[1]

That same “heart-calming” effect is exactly why workouts can feel different:

• Your heart rate may not rise the way it used to, even when you push harder. ^[2]
• You may feel fatigue sooner, especially with vigorous activity. ^[3]
• You may notice a lower resting heart rate (sometimes quite low compared to your pre-medication baseline). ^[4]

The good news: exercise is still beneficial while taking beta blockers, but you often need to adjust how you track intensity and know which symptoms deserve medical attention. ^[2]

People often search for: “beta blocker fatigue during exercise,” “low heart rate on beta blockers while working out,” and “why can’t I get my heart rate up on beta blockers.” Let’s break down the most common issues.

Fatigue is one of the most frequently reported side effects of beta blockers. ^[3]

Some people describe it as:

• Needing longer warm-ups
• Feeling “flat” or underpowered
• Legs tiring quickly on stairs, hills, or intervals
• A sudden drop in performance at intensities that used to feel manageable

A classic explanation is that beta blockers reduce the heart’s normal ability to speed up during exertion, so your body may deliver exercise intensity differently than you’re used to. Mayo Clinic also lists “extreme tiredness” as a common side effect. ^[5]

Important nuance: Fatigue often improves over time as your body adapts, but persistent or worsening fatigue—especially with dizziness, breathlessness, or chest symptoms—should not be brushed off. ^[6]

Beta blockers intentionally lower heart rate. The American Heart Association notes that beta blockers slow the heartbeat and that people may need to adjust how they monitor exercise intensity. ^[1]

A lower pulse can also show up when you check your resting heart rate; the American Heart Association explains that a heart rate under 60 beats per minute can be bradycardia and may also occur from medications such as beta blockers. ^[4]

What’s “too low”?
There isn’t one number that fits everyone. A low heart rate can be normal in trained athletes or during sleep, and medication-related lowering is expected. ^[4]

What matters more is low heart rate plus symptoms. Symptoms that can signal clinically significant bradycardia include dizziness, fainting or near-fainting, confusion, shortness of breath, chest pain, and tiring easily during exercise. ^[7]

This is one of the most common concerns—and it’s very real.

Mayo Clinic explains that beta blockers can keep your heart rate from rising normally during exercise, meaning you might not reach your usual target heart rate even when you work hard. ^[2]

The American Heart Association similarly notes you may need to adjust your target heart rate while on beta blockers. ^[1]

This does not automatically mean your workout is ineffective. Mayo Clinic explicitly states that even if you never reach your previous target heart rate, exercise can still help your heart. ^[2]

These symptoms can happen if your heart rate and blood pressure response is too blunted for the intensity you’re attempting—or if you’re dehydrated, under-fueled, or changing doses.

The National Health Service lists feeling tired, dizzy, or lightheaded as common side effects and notes they can be signs of a slow heart rate. ^[8]

If you get repeated episodes during exercise, that’s a strong reason to call your clinician. Cleveland Clinic also advises contacting your provider for multiple episodes of dizziness or lightheadedness, fainting, chest pain, shortness of breath, or palpitations. ^[6]

Some beta blockers can worsen breathing symptoms in susceptible people, particularly non-selective beta blockers. Mayo Clinic notes that beta blockers are generally not used in asthma due to concerns they may trigger severe asthma attacks. ^[5]

A National Health Service hospital resource similarly warns that beta blockers may worsen asthma and advises checking with a clinician. ^[9]

If you develop new wheeze, chest tightness, or unusually limiting breathlessness during workouts after starting a beta blocker, contact your clinician promptly. ^[6]

Beta blockers reduce the effects of adrenaline-like hormones on the heart. Cleveland Clinic explains they slow your heart rate and reduce stress on the cardiovascular system. ^[6]

When you exercise, your body typically increases heart rate and contractility to meet higher oxygen demands. Beta blockers partially block that response, so you may experience:

• Blunted heart rate rise (you work harder but the pulse won’t climb much) ^[2]
• Earlier perceived exertion (exercise “feels harder” sooner) ^[2]
• Different performance curve (steady efforts may feel okay, but high-intensity bursts feel unusually punishing)

Large exercise physiology data also show measurable reductions in heart rate response during exertion in people on beta blockers. ^[10]

If you used heart rate zones before, beta blockers can make those targets misleading. Both the American Heart Association and Mayo Clinic recommend alternative intensity monitoring approaches.

Mayo Clinic recommends using a perceived exertion scale such as the Borg Rating of Perceived Exertion Scale, where you judge intensity based on effort, breathing, and fatigue. ^[2]

A simple way to apply this:

• Easy: you can speak full sentences comfortably
• Moderate: you breathe harder but can still talk (this is often where many cardio workouts should live) ^[1]
• Hard: speaking more than a few words is difficult

The American Heart Association also describes moderate intensity as breathing harder than normal but still being able to talk. ^[1]

Because beta blockers affect people differently, Mayo Clinic notes that an exercise stress test can help measure how your heart responds and help your care team guide safe targets. ^[2]

The American Heart Association similarly mentions a brief stress test may help determine a new target heart rate. ^[1]

• Longer warm-up and cool-down
• Fewer all-out intervals until you know your response
• Hydration and adequate fueling before longer sessions
• Avoiding sudden posture changes mid-workout if you’re prone to lightheadedness
• Tracking symptoms (what intensity, what time into the workout, what the pulse was, and how quickly symptoms resolved)

You don’t need to panic about every tired day. But you should call your clinician if workout side effects are persistent, worsening, or scary.

Cleveland Clinic recommends reaching out if you have a sudden change in symptoms or side effects, including shortness of breath, chest pain, palpitations, fainting, or repeated dizziness/lightheadedness. ^[6]

Call your clinician soon (same day or within 24–48 hours) if you have:

• New or worsening exercise intolerance that limits normal daily activity
• Recurrent dizziness or near-fainting during or after workouts ^[6]
• Resting heart rate that is much lower than your usual baseline with symptoms (weakness, confusion, breathlessness) ^[7]
• New wheezing or worsening asthma symptoms after starting a beta blocker ^[5]

• The beta blocker name and dose, and when you take it
• Resting pulse trends and what your pulse does during symptoms
• Any blood pressure readings if available
• Exactly what you were doing when symptoms began
• Whether symptoms stop with rest and how fast
• Any chest pain, palpitations, or shortness of breath

Low heart rate becomes an emergency when it’s paired with concerning symptoms or is severely low for you.

Cleveland Clinic advises emergency care if you have a low heart rate with symptoms such as chest pain, palpitations, trouble breathing, or dizziness, or if your heart rate falls below 40 beats per minute and that is not usual for you. ^[11]

The American Heart Association also advises calling emergency services if your heart rate is suddenly very high or very low for you, especially with symptoms such as chest pain, shortness of breath, dizziness, or fainting. ^[4]

Go to emergency care (or call your local emergency number) if you have:

• Chest pain or pressure
• Fainting or near-fainting
• Severe shortness of breath
• Confusion or collapse
• Very low pulse for you, especially with symptoms ^[11]

(Your local emergency number may differ by country; use your region’s emergency services.)

One reason beta blockers matter during exercise is that they can reduce adrenergic symptoms such as rapid heartbeat and tremor—signals some people rely on to notice hypoglycemia. An American Heart Association journal article notes early hypoglycemia signs like tachycardia and tremulousness can be masked. ^[12]

A National Health Service hospital leaflet also warns that in diabetes, beta blockers can affect how you feel during low blood sugar and may require more frequent monitoring when starting. ^[9]

Practical takeaway: If you use insulin or medicines that can cause hypoglycemia, talk to your clinician about workout fueling and consider checking glucose more strategically around exercise.

As noted earlier, some beta blockers may worsen asthma, and Mayo Clinic cautions against their use in asthma in many cases. ^[5]

If breathing symptoms change after starting beta blockers, do not “train through it.” Call your clinician. ^[6]

A lower resting heart rate can be normal in trained people, and medications can lower it further. The American Heart Association notes low resting heart rate can be common in athletes and can also occur due to beta blockers. ^[4]

Here, symptom context matters most: if you feel fine, your clinician may simply monitor. If you feel weak, dizzy, or faint, that’s different. ^[7]

Many people ask: “Should I take my beta blocker before exercise?” There isn’t one universal answer because timing depends on why you’re taking it (arrhythmia control vs blood pressure vs angina vs heart failure), the specific medicine, and how your symptoms behave.

What’s safe to say:

• If workouts consistently feel worst at a certain time after your dose, tell your clinician—timing adjustments are sometimes considered.
• Do not self-adjust doses without medical guidance.

This point matters enough to state plainly: do not abruptly stop a beta blocker because you don’t like how workouts feel.

The National Health Service warns it’s important not to stop beta blockers without your doctor’s advice because suddenly stopping may worsen your condition. ^[8] Mayo Clinic also states you should not suddenly stop a beta blocker because doing so could increase the risk of a heart attack or other heart problem. ^[5]

If side effects are unacceptable, the right move is a clinician conversation about:

• Dose adjustment
• Switching to a different beta blocker
• Considering an alternative medication class (when appropriate)

The American Heart Association even notes that if you’re concerned about exercise effects, your health professional may consider a different beta blocker or medication with less impact on heart rate. ^[1]

“Is it normal to feel weaker at the gym on beta blockers?”

It can be common, especially early on. Fatigue and reduced exercise heart rate response are known effects. ^[2] But if weakness is sudden, severe, or paired with dizziness, fainting, chest pain, or breathlessness, contact your clinician. ^[6]

“What is a safe heart rate during exercise on beta blockers?”

There isn’t a single number that fits everyone because the medication changes heart rate response unpredictably. Mayo Clinic recommends perceived exertion tools and notes stress testing can help define safe targets. ^[2]

“Should I avoid high-intensity exercise on beta blockers?”

Not necessarily, but you may need a slower progression and better symptom monitoring. The main issue is that heart rate zones may not reflect true intensity, so perceived exertion and talk-test cues become more important. ^[2] If high intensity triggers dizziness, chest symptoms, or near-fainting, stop and get medical guidance. ^[11]

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