Skeletal muscle hypertrophy and enhanced mitochondrial bioenergetics following electrical stimulation exercises in spinal cord injury: a randomized clinical trial

European Journal of Applied Physiology, 2025 · DOI: https://doi.org/10.1007/s00421-024-05661-6 · Published: November 22, 2024

Spinal Cord Injury Genetics Rehabilitation

Simple Explanation

This study investigates how different types of electrical stimulation exercises affect muscle and energy production in people with spinal cord injury (SCI). The researchers compared neuromuscular electrical stimulation combined with resistance training (NMES-RT) followed by functional electrical stimulation-lower extremity cycling (FES-LEC) against passive movement training (PMT) combined with FES-LEC. The NMES-RT group did resistance exercises with electrical stimulation for 12 weeks, then cycling with electrical stimulation for another 12 weeks. The PMT group had their legs passively moved for 12 weeks, followed by 12 weeks of cycling with electrical stimulation. The main finding was that building muscle, whether through NMES-RT or PMT combined with FES-LEC, helped improve the function of mitochondria, which are essential for energy production in cells. The NMES-RT group saw an increase in the activity of a specific mitochondrial component.

Study Duration

24 weeks

Participants

32 adults with chronic SCI

Evidence Level

Level 1, Randomized clinical trial

Key Findings

1
Both interventions demonstrated a time effect on CS (P = 0.001) with interaction between both groups (P = 0.01).
2
A time effect was noted in Complex II (P = 0.023; η2 p = 0.15) following both NMES-RT + FES and PMT + FES.
3
NMES-RT + FES increased CIII at P1 compared to BL (P = 0.023; 50%) without additional changes in P2 compared to P1 (P = 1.0; − 3.5%) or BL (P = 0.23; 44%).

Research Summary

This study aimed to determine whether evoking knee extensor (KE) muscle hypertrophy prior to FES-LEC training would further augment mitochondrial enzymatic activity than simply using FES-LEC only. The major finding of the current work is that skeletal muscle hypertrophy either via NMES-RT + FES or PMT + FES is a key determinant of increasing mitochondrial bioenergetics as measured by CS, a marker of mitochondrial density, and complexes (CII, CII + DUQ and CIII) in persons with SCI. Our results indicated a very low complex I activity which is the entry gate for the oxidation of substrates by ETC. Additionally, our training paradigms suggested that evoking muscle hypertrophy via either NMES-RT or FES-LEC may potentially enhance mitochondrial density and mitochondrial ETC activities (Complexes II and III).

Practical Implications

Enhancing Mitochondrial Function

Electrical stimulation exercises, particularly NMES-RT, can be used to enhance mitochondrial function in individuals with SCI, potentially improving their metabolic health.

Muscle Hypertrophy Importance

The study highlights the importance of muscle hypertrophy in improving mitochondrial bioenergetics in SCI patients. Therapies focused on muscle growth may have significant benefits.

Home-Based Therapy Potential

NMES-RT may offer a safe and effective home-based therapy option for enhancing mitochondrial bioenergetics in individuals with SCI, reducing the need for expensive equipment.

Study Limitations

1
The study did not measure mitochondrial respiration due to limited resources.
2
Complex IV was not measured due to limited muscle biopsy size.
3
The SCI population is heterogeneous in nature as result of wide age range, level of injury and severity of injury.

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