5.3 Resting Heart Rate, Blood Pressure, BMI, and Waist-to-Hip Ratio

Physiological Baselines Guide Safe Testing

After subjective screening, NASM collects objective physiological measures: resting heart rate, blood pressure, and body-size/composition indicators. These are screening and trend data, not diagnoses. They tell the trainer whether it is safe to proceed to harder testing, give a starting point for intensity prescription, and create a baseline that reassessment can compare against. Abnormal or symptomatic values trigger referral or clearance — never a diagnosis from the trainer.

Resting heart rate (RHR)

Measure RHR ideally first thing in the morning or after several minutes of seated rest, palpating the radial or carotid pulse for 30 or 60 seconds. A normal resting heart rate is 60-100 beats per minute (bpm). Below 60 bpm is bradycardia; above 100 bpm is tachycardia. Well-trained endurance clients commonly sit below 60 bpm as a healthy adaptation, so context matters. RHR also feeds the Karvonen formula, so an accurate value is worth taking carefully.

Blood Pressure (2017 ACC/AHA Categories)

Blood pressure (BP) is recorded as systolic over diastolic in mm Hg using a properly sized cuff on a seated, rested client. NASM aligns with the 2017 American College of Cardiology / American Heart Association (ACC/AHA) classification:

The trainer's role is to measure, interpret conservatively, and refer when indicated — not to medicate or diagnose. A reading of 146/92 mm Hg accompanied by headache and dizziness is in the Stage 2 range with symptoms, so the correct action is to stop testing and refer for medical evaluation rather than proceed. A single elevated reading without symptoms is a cue to recheck and monitor; persistently high values warrant clearance.

Target Heart Rate: Karvonen vs. 220 − Age

To set cardio intensity, NASM teaches two ideas the exam loves to contrast.

Estimated maximum heart rate uses the well-known formula HRmax = 220 − age. It is fast but only a population average: individual HRmax has a standard deviation of roughly ±10-12 bpm, so for a given person the estimate can be off enough to drop them into the wrong training zone entirely. It also breaks down for clients on beta-blockers, where measured HR is artificially blunted.

The Karvonen method (heart-rate-reserve, HRR) is more individualized because it incorporates resting heart rate:

Target HR = ((HRmax − HRrest) × %intensity) + HRrest

Worked example: a 40-year-old with RHR 65, training at 70% intensity. HRmax = 220 − 40 = 180. HRR = 180 − 65 = 115. THR = (115 × 0.70) + 65 = 80.5 + 65 ≈ 146 bpm. Because Karvonen anchors to the client's own resting HR, it produces a more accurate zone than simply taking 70% of HRmax (which would give 126 bpm). When formulas are unreliable, fall back on RPE and the talk test.

BMI, Waist-to-Hip Ratio, and Circumference

Body Mass Index (BMI) = weight in kilograms divided by height in meters squared (kg/m²). Standard adult categories:

BMI is quick and population-useful but cannot distinguish muscle from fat — a muscular athlete can register "overweight" while carrying little body fat. That is why NASM says to pair BMI with other measures.

Waist-to-hip ratio (WHR) = waist circumference ÷ hip circumference, capturing central (abdominal) fat distribution, which carries higher cardiometabolic risk. Commonly cited higher-risk thresholds are roughly ≥ 0.90 for men and ≥ 0.80-0.85 for women. Circumference measurements (waist, hips, arms, thighs) are cheap, low-tech trend tools that track change over time when taken at consistent landmarks. Together these measures give the context BMI alone lacks.

Putting the resting measures together

None of these numbers is a diagnosis. The trainer uses them to (1) decide whether it is safe to proceed to harder testing, (2) set a conservative starting intensity, and (3) establish a baseline for reassessment. A clean RHR, a Normal-to-Elevated BP, and a moderate WHR support proceeding with standard assessments; a symptomatic high BP, a resting tachycardia, or a cluster of risk factors points toward clearance first. Because all four measures feed later comparisons, the trainer records them carefully and re-takes them under matched conditions each time. Worked intensity targets (via Karvonen) are then layered on top of a safe baseline rather than guessed.

Measurement technique matters as much as the numbers. For blood pressure, the client should be seated and rested several minutes with feet flat and arm supported at heart level, using a cuff sized to the arm; an undersized cuff falsely raises the reading. For resting heart rate, take the pulse when the client is calm and has not recently consumed caffeine or exercised. Sloppy technique creates artifacts that look like real change at reassessment, so consistency is the trainer's best defense against misleading data.