Accuracy of Heart Rate Measurement by the Fitbit Charge 2 During Wheelchair Activities in People With Spinal Cord Injury: Instrument Validation Study

JMIR Rehabil Assist Technol, 2022 · DOI: 10.2196/27637 · Published: January 19, 2022

Spinal Cord Injury Assistive Technology Rehabilitation

Simple Explanation

Heart rate (HR) is an important and commonly measured physiological parameter in wearables. In individuals with spinal cord injury (SCI), blood pressure control is often altered and could therefore influence HR accuracy measured by the PPG technique. The objective of this study is to investigate the HR accuracy measured with the PPG technique with a Fitbit Charge 2 (Fitbit Inc) in wheelchair users with SCI, how the activity intensity affects the HR accuracy, and whether this HR accuracy is affected by lesion level.

Study Duration

Not specified

Participants

48 participants, 38 with SCI and 10 without SCI

Evidence Level

Instrument Validation Study

Key Findings

1
HR measured with the PPG technique showed lower accuracy in people with SCI than in those without SCI.
2
The accuracy was just above the acceptable level in people with paraplegia, whereas in people with tetraplegia, a worse accuracy was found.
3
The accuracy seemed to worsen with increasing intensities. Therefore, high-intensity HR data, especially in people with cervical lesions, should be used with caution.

Research Summary

With an overall MAPEall lesions of 12.99%, the accuracy fell below the standard acceptable MAPE of –10% to +10% with a moderate agreement (concordance correlation coefficient=0.577). The HR accuracy of Fitbit Charge 2 seems to be reduced in those with cervical lesion level in all activities (MAPEno SCI=8.09%; MAPE<T5=11.16%; MAPET1−T5=10.5%; and MAPE>T1=20.43%). The accuracy of the Fitbit Charge 2 decreased with increasing intensity in all lesions (MAPErest=6.5%, MAPEactivity=12.97%, and MAPEstrength=14.2%).

Practical Implications

Caution with PPG-based HR Measurements

PPG-based HR measurements during activities should be taken with caution in people with SCI, especially in those with cervical SCI lesions.

Limited Use for Medical Purposes

It is advised to avoid using PPG-based HR measurements for medical purposes in people with SCI with a cervical lesion level (>T1).

Global Impression of Exercise Intensity

Outcomes can still be of value in situations where the consequences of inaccurate HR data are low, for example, to get a global impression of energy expenditure and exercise intensity during physical activities in daily life.

Study Limitations

1
The reference device used, a Polar H7 HR monitor, is not considered a gold standard.
2
HR outcomes from both devices were provided without raw signals (raw ECG signals and interbeat intervals).
3
No information was collected on the environmental conditions or skin information that could possibly affect the PPG signal

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