The Beta-Blocker and the Meaningless Heart-Rate Target
Marcus, 54, is a software manager who has signed up for a 10 km road race in 20 weeks. His physician has cleared him for moderate-to-vigorous exercise. He takes 50 mg metoprolol succinate daily for hypertension; his resting blood pressure is 138/86 mmHg and his resting heart rate is 56 bpm. He is 178 cm, 98 kg, and has not exercised regularly in 12 years.
Using 220 minus age, Marcus calculated a maximum heart rate of 166 bpm and decided to run at 70% of that, about 116 bpm. At his first supervised session he held 116 bpm for 25 minutes on the treadmill at 6.5 km/h and 2% incline, then said the effort felt "easy - I could have talked the whole time." When he stepped off the treadmill he felt briefly lightheaded. He now wants to add a fourth running day and asks whether he should buy a watch that alerts him whenever he drifts above 116 bpm.
1. What is wrong with Marcus's heart-rate target, and what should you use in its place?
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The number is meaningless for him. Age-predicted formulas already carry a standard deviation of roughly ±10–12 bpm, so 166 is a population average, not Marcus's maximum. Metoprolol then blunts the heart-rate response: beta-1 blockade lowers resting heart rate and typically caps exercise heart rate well below what the same workload would produce unmedicated - often 20–30 bpm lower at submaximal intensities. So 116 bpm is not 70% of his maximum; it may be closer to 60–65%. That is exactly why the effort felt "easy."
What to use instead: the talk test and RPE. He should be working at 12–14 on the 6–20 Borg scale - "somewhat hard," able to speak in short sentences but not to sing. Heart rate becomes a trend line to observe, not a prescription to obey. If he wants a real number, a supervised submaximal test with the medication recorded, or a physician-supervised maximal test, is the sound route - and that decision sits with his physician, not with you.
Do not simply add 30 bpm to compensate; the blunting is not a fixed offset and varies with dose, timing, and workload. Reset his zones from the talk test and progress by duration first, intensity second.
2. Explain the lightheadedness when he steps off the treadmill, and describe what you change in how the session is built and monitored.
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Beta-blockade reduces the tachycardic compensation for venous pooling, so when Marcus stops abruptly, blood stays in his legs and his systolic pressure dips - post-exercise orthostatic hypotension, made more likely by dehydration and a warm room.
Session design changes:
- Graduated cool-down: 3–5 minutes of easy walking or cycling after the main set. Never let him step straight off a treadmill and stand still.
- Teach the muscle pump: calf and glute contractions before he stands; if symptoms start, sit with his head down rather than trying to walk it off.
- Hydration and heat: weigh him before and after a summer session; 1 kg lost is roughly 1 L of fluid. Keep the room cool and avoid hot outdoor runs until tolerance builds.
- Breathing: no breath-holding under load. A Valsalva raises BP sharply and then drops it, which is the last thing he needs on an antihypertensive.
- Document: BP and HR before and after, plus any symptoms, every session. A single brief episode after hard effort is common; recurrent dizziness, fainting, chest pain, or unusual breathlessness goes back to his physician before you progress intensity.
Also ask, without judgement, whether he ever skips a dose to "feel more energetic." That is a common and genuinely dangerous behaviour with antihypertensives.
3. At week 8 his resting heart rate has risen from 56 to 68 bpm. What do you consider, and what do you do this week?
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Consider four possibilities, in this order:
- Medication adherence or a changed prescription - a missed or reduced metoprolol dose unmasks his own resting heart rate. Ask directly and send him to his physician rather than guessing.
- Illness or under-recovery - a low-grade infection, poor sleep, alcohol, or accumulated fatigue raises resting heart rate by 5–10 bpm. Compare against his session RPE and whether his pace at a given effort has dropped.
- Dehydration or heat - plasma volume loss raises heart rate at any given workload.
- Aerobic adaptation - this normally lowers resting heart rate, so a rise is a flag, not a win.
This week: hold intensity where it is, keep sessions at RPE 11–13, and have him measure resting heart rate on three consecutive mornings, same time, before getting out of bed. Ask about caffeine, energy drinks, and night-shift-like sleep patterns. If it stays elevated beyond 7–10 days, or is paired with breathlessness, chest discomfort, or unusual fatigue, refer back to his physician before continuing to progress. Write the whole exchange into the session note - if he later has an event, your record is what shows you noticed and acted.