In recent years, electrical muscle stimulation (EMS) devices have emerged as a novel, attractive, and time-saving complementary training technique for physical fitness and rehabilitation. While EMS training is known to improve muscle mass and strength, most studies have focused on the elderly or specific patient populations. This article delves into the science behind EMS, its potential benefits for weight loss, and what the research reveals about its effectiveness.
Understanding Electrical Muscle Stimulation (EMS)
EMS is a method that uses electrical impulses delivered through various forms of electrical current to electrodes on the target muscle. The electrical current causes involuntary muscle contraction, produces adaptations through non-selective synchronous recruitment of muscle fibers, and enables greater motor unit activation by increasing the pulse firing rate, resulting in exercise-like effects. Repeated EMS sessions on muscles have been reported to increase capillary flexibility and blood flow in muscle fibers.
How EMS Works for Weight Loss
One of the key reasons that EMS is effective for weight reduction is because it aids in the creation of a calorie deficit, which is the primary means of losing weight. You may do this by reducing your calorie intake, exercising to burn more calories, or a combination of the two. EMS is believed to have a significant impact on reducing body fat by increasing the resting metabolic rate, leading to sustained reductions in body fat. This effect may be attributed to increased physical activity, which is associated with improved lipoprotein profiles and increased fat oxidation.
Research Findings on EMS and Weight Loss
Studies on Abdominal Obesity
A randomized, double-blind, sham-controlled trial investigated the effects of EMS on abdominal obesity. The electrical muscle stimulation group achieved a mean 5.2±2.8 cm decrease in waist circumference while the transcutaneous electrical nerve stimulation group showed only a 2.9±3.3 cm decrease (P=0.005). About 20 (70.0%) of the electrical muscle stimulation group lost more than 4 cm of waist circumference but that only 8 (33.3%) of the transcutaneous electrical nerve stimulation group did so (P=0.008). Furthermore, fasting free fatty acid levels were significantly higher in the electrical muscle stimulation than in the transcutaneous electrical nerve stimulationgroup at week 12 (P=0.006). In the electrical muscle stimulation group, slight decreases in visceral abdominal fat and total abdominal fat areas by computer tomography were observed at 12 weeks, but these decreases were not significant.
EMS Combined with Resistance Training
One study investigated the effects of frequency-specific EMS combined with resistance exercise training for 8 weeks on muscle mass, strength, power, body composition, and parameters related to exercise fatigue. The results showed that resistance exercise training combined with daily EMS significantly improved muscle mass (p = 0.002) and strength (left, p = 0.007; right, p = 0.002) and significantly reduced body fat (p < 0.001) than the no EMS group. However, there was no significant advantage for biochemical parameters of fatigue and lower body power.
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EMS for Activating Abdominal Muscles
For non-athletes, topical EMS application is effective in activating superficial abdominal muscles and increasing the cross-sectional area of the lateral abdominal wall and rectus abdominis.
Contradictory findings
After eight weeks of EMS "training,” subjects experienced no significant changes in weight, body-fat percentage, strength or overall appearance. Some subjects also reported that the EMS sessions were painful when high levels of stimulation were used.“In-home EMS has little practical significance or carryover benefit,” adds Dr. Porcari.
The Importance of Combining EMS with Exercise
While both traditional resistance exercise training and EMS training have the potential to improve muscle mass and athletic performance, it appears that a combination of the two offers greater benefits.
Parameters and Protocols
The gains in muscle strength or mass may still be influenced by the specific protocols and frequency of use. The frequency parameter of pulse stimulation seems to have different effects and benefits on different muscle groups and different muscle fibers.
Safety and Feasibility
The safety and effectiveness of EMS are still controversial in practice, and some people think that excessive use of EMS may lead to adverse consequences.
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A Closer Look at a Specific Study
Study Design and Participants
Qualified 14 male and 14 female subjects were included and randomly assigned to two groups with gender parity (seven male and seven female per group): (1) no EMS group, (2) daily EMS group (quadriceps, abdominal muscles, biceps, twice a day, 30 min each time). The mean age (no EMS group: 21.6 ± 1.7; daily EMS group: 21.8 ± 2.0), height (no EMS group: 168.8 ± 11.8 cm; daily EMS group: 167.8 ± 9.9 cm) and weight (no EMS group: 64.2 ± 14.4 kg; daily EMS group: 68.5 ± 15.5 kg) of the two groups of subjects were very similar with no significant difference. All subjects underwent intervention for 8 consecutive weeks and performed resistance exercise training three times a week.
EMS Protocol
EMS electrodes were attached to the biceps of both hands, the abdomen, and the quadriceps of both legs sequentially. Each part was stimulated once a day for 30 min.
Resistance Training
All subjects performed resistance training three times a week to strengthen their upper limbs, back, abdomen, and legs, respectively, using a pneumatic resistance training machine including Abs/Abduction 3520-HI5, Push-up/Pulldown 3120, Ab/Back 5310, Torsion Rehab 5340, Leg Extension/Curl 3530, and Leg Press 5540 (AB Hur Oy, Kokkola, Finland). Before beginning training, all subjects evaluated their own 3RM and calculated their 1RM according to the coefficient formula in previous literature, which was used as the standard for setting subsequent resistance training intensity. After a pre-exercise warm-up, all subjects performed one set of 15 repetitions at 60% of 1RM intensity in the first week and one set of 12 repetitions with resistance increased to 70% of 1RM intensity in the second week.
Measurements
The InBody 570 device (In-body, Seoul, South Korea) is a bioelectrical impedance analyzer (BIA) that measures impedance at 1, 5, 50, 260, 500, and 1,000 kHz by the multi-frequency principle and was used in this study to measure body composition. All subjects were assessed VO2max by an automatic breathing analyzer (Vmax 29c; Sensor Medics, Yorba Linda, CA, USA) and on a treadmill (Pulsar; h/p/cosmos, Nussdorf-Traunstein, Germany). To assess fatigue-related indicators, subjects fasted for at least 8 h and underwent a fixed-intensity exercise challenge (60% VO2max) with recovery blood sampling at designated time points, including baseline (0), post-exercise 30 min (E30), and rest for 60 min after exercise (R60). Fatigue-related assessments included lactate, ammonia (NH3), and glucose. The aspartate transaminase (AST), alanine aminotransferase (ALT), blood urea nitrogen (BUN), creatinine (CREA), uric acid (UA), and free fatty acid (FFA) were assessed. Before the actual test, participants were instructed to apply minimal force to the grip to ensure a comfortable and standardized gripping distance. The countermovement jump (CMJ) test is widely used to assess lower body speed, strength, and explosiveness.
Results
After 8 weeks of EMS combined with RT, there were no significant differences between the no EMS group and the daily EMS group in terms of body weight, BMI, muscle mass, and fat mass. However, in the no EMS group, there were significant increases in body weight (p < 0.001), BMI (p < 0.001), and fat mass (p < 0.001) after 8 weeks of intervention, compared to before. Both the no-EMS group and the daily EMS group showed a significant increase in left-hand (no-EMS group, 1.03-fold (p = 0.001); daily EMS group 1.09-fold (p < 0.001)) and right-hand grip strength (no-EMS group, 1.04-fold (p < 0.001); daily EMS group 1.12-fold (p < 0.001)) compared to pre-intervention (p < 0.05) in within-group comparisons. However, there were no significant differences between the two groups. There were no significant differences between the no EMS and daily EMS groups in terms of rate of force development (RFD), peak force, and jump height.
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Discussion of the Study
Combining resistance training (RT) with EMS resulted in significant improvements in muscle mass and upper limb muscle strength, while there was only a non-significant trend for lower limb strength. EMS is believed to have a significant impact on reducing body fat by increasing the resting metabolic rate, leading to sustained reductions in body fat. This effect may be attributed to increased physical activity, which is associated with improved lipoprotein profiles and increased fat oxidation.
Limitations of EMS Studies
Several limitations in EMS studies should be considered:
- Study Duration: Studies are often conducted over a relatively short period, such as 12 weeks, which may not be long enough to produce significant differences in certain outcomes like abdominal fat distribution.
- Participant Characteristics: Study cohorts may have specific characteristics (e.g., a small proportion of severely obese subjects or individuals with diagnosed diseases), limiting the generalizability of the results.
- Lack of Combined Interventions: Many studies do not combine EMS with aerobic exercise or dietary programs, which could have synergistic effects on weight loss and metabolic outcomes.
- Variability in EMS Protocols: The specific parameters and protocols used in EMS training can vary widely, making it difficult to compare results across different studies.
- Measurement Issues: Discrepancies between different measurement methods (e.g., waist circumference vs. CT scans) can lead to conflicting results.