Electrical Currents for Muscle Contraction

Vocabulary practice flashcards covering physiology, clinical applications, parameters, contraindications, and case studies for neuromuscular electrical stimulation (NMES) and muscle contraction.

Neuromuscular Electrical Stimulation (NMES)

An electrical modality used to produce muscle contraction that specifically requires an intact and functioning peripheral nervous system.

Reversed Recruitment Order

The physiological difference in NMES where large, fast-twitch type II muscle fibers are recruited before small, slow-twitch type I fibers.

Type II Muscle Fibers

Fast-twitch muscle fibers that produce the strongest and quickest contractions, but fatigue rapidly and undergo the greatest atrophy from disuse.

Disuse Fiber Atrophy Identification

A fresh frozen muscle biopsy showing dark brown/black atrophic type II muscle fibers alongside light beige normal-sized type I fibers.

On:Off Ratio (Fatigue Effect)

The relationship between stimulation and rest time during NMES, showing that longer off-times (such as $1\,\text{sec}$ on to $5\,\text{sec}$ off) prevent rapid fatigue and maintain contraction force over treatment.

Overload Principle in NMES

The principle stating that greater contraction loads yield greater strength gains; in NMES, force is increased by adjusting total current, pulse duration, amplitude, electrode size, and applied resistance.

Specificity Theory in NMES

The concept that electrical stimulation preferentially recruits type II muscle fibers, making NMES especially beneficial for conditions where type II atrophy predominates.

Functional Electrical Stimulation (FES)

The use of electrical stimulation to assist or restore functional activities such as locomotion, hand grasp, respiration, and bowel or bladder management in spinal cord injury.

EMG-Triggered NMES

A technique where patient-initiated voluntary muscle effort triggers electrical stimulation, outperforming NMES alone for upper-extremity stroke recovery.

Electrical Muscle Stimulation (EMS) for Denervated Muscle

Direct stimulation of denervated muscle fibers requiring pulse durations longer than $10\,\text{msec}$ using continuous DC to retard atrophy and fibrosis.

Core NMES Contraindications

Demand pacemakers or unstable arrhythmias, electrode placement over the carotid sinus, active venous thrombosis or thrombophlebitis, and application over the pelvis, abdomen, or low back during pregnancy.

Motor Point

The site on a muscle, generally located near the middle of the muscle belly, where an electrode is placed to achieve the most effective electrical contraction.

Quadriceps Electrode Placement Configuration

Electrodes placed over the proximal and distal ends of the quadriceps muscle belly, positioned parallel to the muscle fiber direction and separated by at least $2\,\text{inches}$.

Stimulus Frequency and Tetany Graph

Demonstration that a stimulus frequency of at least $30\,\text{pps}$ is required to produce a smooth, sustained (tetanic) muscle contraction.

Recommended Clinical Pulse Duration (NMES)

Parameter settings of $150\text{-}200\,\mu\text{s}$ for small muscles and $200\text{-}350\,\mu\text{s}$ for large muscles to produce comfortable muscle contractions.

Strengthening On:Off Ratio

An initial NMES setting of $6\text{-}10\,\text{seconds}$ on and $50\text{-}120\,\text{seconds}$ off (a $1:5$ ratio) to reduce muscle fatigue during high-intensity strength training.

Spasm and Edema On:Off Ratio

An NMES parameter setting of $2\text{-}5\,\text{seconds}$ on and $2\text{-}5\,\text{seconds}$ off (equal $1:1$ ratio) to induce repetitive muscle pumping without long rest intervals.

Ramp Time

The duration over which current amplitude gradually increases or decreases (typically at least $1\text{-}2\,\text{seconds}$), extended to $4\text{-}8\,\text{seconds}$ for antagonist stimulation in spastic patients.

Target Amplitude for Muscle Strengthening

Current intensity adjusted to achieve at least $>50\%$ of Maximum Voluntary Isometric Contraction (MVIC) in uninjured muscle, or at least $>10\%$ MVIC in post-injury recovery.

Hamstring and Quadriceps Strengthening Positioning

Electrode configurations placed over targeted muscle bellies with limb stabilization (e.g., straps and foam rollers) to conduct controlled isometric NMES strengthening.