Electromyography, or EMG, assesses the electrical activity of muscles during contraction. In exercise science, it helps clarify recruitment patterns across movements so researchers and practitioners can better understand mechanics, training efficiency and neuromuscular coordination. Professional strength coaches like Bret Contreras note EMG’s usefulness for informing evidence-based programming across athletic and general populations. Used appropriately, EMG can highlight activation deficits, support targeted interventions and contribute to individualized corrective or performance plans.
Though common in research, EMG has practical value for coaches, physical therapists and trainers. By quantifying muscle activity during tasks, it can help validate exercise selection, sharpen technique and flag compensations that may raise injury risk. In rehabilitation, it can track activation over time and confirm whether target muscles are contributing as intended. EMG complements—not replaces—clinical reasoning and movement assessment.
What EMG measures
EMG records electrical signals when the nervous system activates a muscle, typically via skin-mounted electrodes for noninvasive surface EMG (sEMG) or fine-wire electrodes for intramuscular EMG. In most training contexts, sEMG is used.
Signal amplitude reflects the level of neural drive to the recording site, but it is influenced by electrode placement, normalization method, adipose tissue, muscle depth, movement speed, load and filtering. Higher EMG amplitude generally indicates greater recruitment, but it does not directly equal force output or guarantee a superior training effect.
EMG in exercise comparison studies
EMG is often used to compare exercises for a given muscle. For example, studies frequently report high gluteus maximus activity in hip thrusts—especially near terminal hip extension—relative to some squat or deadlift conditions. That does not make one exercise categorically “better,” but it does suggest different tasks emphasize different joint angles or phases of contraction. When interpreted with context (normalization, technique, load, range of motion), such findings can make programming more precise.
EMG and movement efficiency
Beyond exercise comparisons, EMG can illuminate coordination. In rehab, clinicians use EMG to verify that injured patients recruit intended muscles during tasks such as squatting or walking rather than compensating with adjacent musculature. In sport settings, EMG can help refine sprinting, jumping or lifting mechanics by revealing timing or side-to-side differences that are not obvious visually.
Limitations and interpretation
EMG has well-known limitations. Signals can be affected by crosstalk from nearby muscles, skin impedance, electrode shift, external noise and contraction type (isometric, concentric, eccentric). Load, fatigue and joint angle also change amplitude. Crucially, EMG does not measure force or mechanical tension directly. High EMG does not guarantee greater hypertrophy or strength gains; results are best interpreted alongside kinetics, kinematics and training volume.
EMG in strength programming
When integrated with movement analysis, EMG data can guide exercise selection or sequencing. If a lifter struggles to recruit the glutes in knee-dominant tasks, programming may include hip-dominant options that show higher activity for that individual (for example, bridges or hip thrust variations) and then re-test. Coaches often use EMG-informed insights to place higher-activation accessories where they best serve the session goal.
Research applications and advances
EMG is used across populations to study how training status, age and fatigue affect recruitment patterns, and it informs equipment design and technique modifications. Wearable EMG systems are expanding access to real-time biofeedback in clinics and training halls, though data quality and interpretation still require expertise.
Practical considerations for coaches
For most practitioners, EMG serves as conceptual guidance. Knowing which exercises tend to challenge a target muscle helps shape warm-ups, accessories and cues. Experts like Bret Contreras have underscored that intentional hip drive and focused glute contraction during hip-dominant work help prevent substitution by the spinal extensors or quadriceps—principles that align with EMG evidence showing task- and angle-specific activation. The goal is to use EMG findings to reinforce sound execution, not to chase the highest number without context.
EMG offers objective insight into how muscles behave during movement. Interpreted carefully—and paired with kinetics, kinematics and coaching—EMG can refine exercise selection, technique and training balance. It should enhance movement precision and personalization, not replace fundamental programming principles.