Max HR (pick a formula): \( HR_{\max}^{\text{Fox}} = 220 - \text{age} \) | \( HR_{\max}^{\text{Tanaka}} = 208 - 0.7\,\text{age} \) | \( HR_{\max}^{\text{HUNT}} = 211 - 0.64\,\text{age} \) \( HR_{\max}^{\text{Gulati (women)}} = 206 - 0.88\,\text{age} \) Heart Rate Reserve (HRR): \( HRR = HR_{\max} - HR_{\text{rest}} \) Karvonen target: \( HR_{\text{target}} = HR_{\text{rest}} + \% \times HRR \) AHA zones (by %HRmax): Moderate \( \approx 50\!-\!70\% \), Vigorous \( \approx 70\!-\!85\% \).