I understand that with patients that have a complete spinal cord injury we should not use the age predicted HR formula to calculate their max HR (220-age) due to their inability to achieve that number as their injury makes the results variable; what I do not understand is how I would calculate their max HR? What formula would be appropriate for someone with a thoracic spinal cord injury (as in T3), for example?

When identified, HRmax and another key variable – HRrest, are both used to determine the target HR zone for exercise (AKA exercise intensity).

Due to an attenuated HR response following an impairment of the Autonomic Nervous System (ANS), it may become challenging to evaluate exercise intensity using traditional formulaes that incorporate HR values (such as HRmax). Impairments, in this case, may occur with spinal cord injury, Multiple Sclerosis (MS) or certain pharmacological agents. In these instances, the Rate of Perceived Exertion (RPE) scale then becomes a useful alternative measure for determining exercise intensity. [1] Other alternatives also include continuous ECG or use of Metabolic Equivalents (METs). [2]

It may be difficult to determine HR or HRmax in a T3 SCI patient due to ANS impairment, and if the purpose of determining HRmax is to calculate target heart rate or exercise intensity, then the literature provides us with other alternatives.

Reference 1: Miller PD. Fitness Programming and Physical Disability. Human Kinetics Publishers, 1995. Chapter 5; Exercise Prescription: Adapting Principles of Conditioning. Pg 72., Reference 2: Giles SM. PTExam: The Complete Study Guide. 2013. Chapter 6; Cardiovascular/Pulmonary and Lymphatic System. Pg 290.