Beta-Blockers, Heart Rate, and a Pre-Workout Tub
Marcus, 52, has taken your 6:00 a.m. indoor cycling class twice a week for four months. At the start of today's class he mentions that his doctor recently added metoprolol to his existing lisinopril and that his resting heart rate has dropped from 68 to 54 bpm. He wears a wrist optical heart-rate monitor and wants you to tell him his 'target zone,' because he read that he should train at 70-80% of his maximum. During the warm-up his monitor reads 118 bpm while he describes the effort as 'maybe a 7 out of 10,' and he says he feels slightly lightheaded when he stands to adjust his seat. He also asks whether he should start the 300 mg caffeine pre-workout his coworker gave him, and whether a 'thermogenic' fat burner would help him lose the 15 pounds he gained over the winter. The class is 45 minutes, you have 18 participants, and the room is warm.
1. How do you set Marcus's intensity for today's class, and what do you tell him about the '70-80% of maximum' rule?
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Start with what the medications do, not with a formula. Metoprolol is a beta-blocker and blunts both resting and exercise heart rate, so an age-predicted maximum (220 - 52 = 168 bpm) and any percentage-based zone built on it will not describe him. His true maximum is likely well below that prediction, and his heart rate at a given workload may sit far under the chart. Lisinopril adds a hypotension risk, which fits his lightheadedness on standing.
Switch to effort-based anchors. Keep him at an RPE of about 4-6 out of 10, at a level where he can still speak in short sentences (talk test). Those anchors stay valid when heart rate is pharmacologically altered; the number on the monitor does not.
Treat the wrist monitor as a trend, not a target. Optical wrist sensors lag behind rapid workload changes and lose accuracy with sweat and gripping. The 118 bpm reading at '7 out of 10' is probably not his true exercise heart rate.
Stay in scope and document. I do not prescribe a target heart rate. I explain that the guideline assumes no rate-limiting medication and suggest he ask his cardiologist or pharmacist for a personal range. Today I modify: seated climbs instead of standing attacks, no breath-holding, water within reach, and a check-in at the 15-minute mark. If the lightheadedness recurs, he stops and follows up medically.
2. How do you handle the caffeine pre-workout and the fat-burner question without giving medical or supplement advice?
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Separate the two products, then separate what I can say from what I can't.
Caffeine. 300 mg is within the range studied for performance (roughly 3-6 mg/kg), but it is a large single dose to debut, and he is hypertensive on two medications. General guidance of up to about 400 mg/day is for healthy adults, not a green light for him. Caffeine raises heart rate and blood pressure acutely, and a proprietary pre-workout blend can hide other stimulants on the label, so I genuinely do not know what he would be taking.
What I actually say: I can describe general effects and general upper limits; I cannot clear him, dose him, or recommend a brand. My advice is to bring the label to his pharmacist or physician first, and not to test a new stimulant on a class day when he is already reporting lightheadedness.
Fat burner. Same scope answer plus a reality check. The 15 pounds came from an off-season shift in intake and activity, not from a missing pill; stimulant-based thermogenics carry cardiovascular risk for modest, poorly sustained effects. I point him at levers he controls - a modest calorie deficit, protein at meals, sleep, and the two classes he already attends - and, if he wants structured help, a referral to a registered dietitian.
Why not just say 'ask your doctor' and move on? Because he asked me, and a useful answer plus a referral is more likely to be followed than a deflection.