Low-Force Muscle Activity Regulates Energy Expenditure after Spinal Cord Injury

Abstract

Reduced physical activity is a primary risk factor for increased morbidity and mortality. People with spinal cord injury (SCI) have reduced activity for a lifetime, as they cannot volitionally activate affected skeletal muscles. We explored whether low-force and low-frequency stimulation is a viable strategy to enhance systemic energy expenditure in people with SCI.

Purpose: This study aimed to determine the effects of low stimulation frequency (1 and 3 Hz) and stimulation intensity (50 and 100 mA) on energy expenditure in people with SCI. We also examined the relationship between body mass index and visceral adipose tissue on energy expenditure during low-frequency stimulation.

Methods: Ten individuals with complete SCI underwent oxygen consumption monitoring during electrical activation of the quadriceps and hamstrings at 1 and 3 Hz and at 50 and 100 mA. We calculated the difference in energy expenditure between stimulation and rest and estimated the number of days that would be necessary to burn 1 lb of body fat (3500 kcal) for each stimulation protocol (1 vs 3 Hz).

Results: Both training frequencies induced a significant increase in oxygen consumption above a resting baseline level (P < 0.05). Energy expenditure positively correlated with stimulus intensity (muscle recruitment) and negatively correlated with adiposity (reflecting the insulating properties of adipose tissue). We estimated that 1 lb of body fat could be burned more quickly with 1 Hz training (58 d) as compared with 3 Hz training (87 d) if an identical number of pulses were delivered.

Conclusion: Low-frequency stimulation increased energy expenditure per pulse and may be a feasible option to subsidize physical activity to improve metabolic status after SCI.

Conflict of interest statement

Conflict of Interest:

There are no conflicts of interest.

The results of this study do not constitute endorsement by the American College of Sports Medicine.

The results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

Figures

Figure 1

Representative example of oxygen consumption. Baseline measurements (“No Stimulation”) were taken before, between, and after stimulation at 1 Hz and at 3 Hz. For each participant, the last 12 measurements (representing 6 minutes) of each stage were averaged.

Figure 2

Metabolic response to stimulation. A) Oxygen consumption increased as a function of stimulation frequency. * = higher than baseline (p = 0.001); # = higher than 1 Hz (p 0.05). C) Based on measured oxygen consumption (see text for energy expenditure calculation), days to burn 1 pound of fat increased with frequency. * = higher than 1 Hz (p

Figure 3

Effect of stimulation intensity. Oxygen consumption increased as a function of stimulation intensity. * = higher than baseline and 50 mA (p = 0.001).

Figure 4

Effect of body habitus: A) BMI negatively correlated with the change in oxygen consumption when applying 1 Hz stimulation (r2=0.57) and 3 Hz stimulation (r2=0.62). B) VAT negatively correlated with the change in oxygen consumption when applying 1 Hz stimulation (r2=0.47) and 3 Hz stimulation (r2=0.56).