The Vibro-Twist




Electric Muscle Stimulation – An Athletic Advantage?

Electric muscle stimulation (EMS), also known as neuromuscular electrical stimulation (NEMS) or percutaneous electrical stimulation (PES), is a method of eliciting muscle activity through applied electrical current. Your muscles naturally contract in response to electrical signals sent from your brain, and EMS replicates this with electrodes placed on the skin and a current run through them from a power source (Figure 1).

Figure 1. An example of an EMS unit with the electrodes (pads) placed on the quadriceps muscles

There are a couple of interesting physiological differences between a voluntary contraction through the central nervous system and an involuntary contraction through EMS. First, while a voluntary contraction will recruit smaller motor units and slow-twitch, Type-I fibers first and then activate the Type-II fibers as needed, an EMS contraction reverses this order. Because the involuntary contraction bypasses this neurological coordination, and because the applied current flows more easily through the larger neurons of the fast-twitch fiber, they are activated immediately, a response that is impossible to achieve through our own volition. Second, a voluntary contraction activates individual fibers in relays in order to conserve energy and not tire too quickly; EMS activates all of the motor units in the area at the same time, contracting all of the fibers with no holding back.

For much of the 20th century, EMS was used for orthopedic rehabilitation and physical therapy, specifically neuromuscular reintroduction and prevention of atrophy. However, it wasn’t until a Soviet scientist presented to the West in 1973 what Communist Bloc countries had been doing for 2o years: EMS as a method of strength training. Dr. Y. Kots of the Central Institute of Physical Culture in the USSR claimed to see up to 30-40% strength gains in already-trained individuals using specific methods of EMS, and while these results are quite extreme and have not been replicated in Western studies, the years of research since have shown that training with EMS leads to greater increases in isokinetic peak torque, maximal isometric strength, and maximal dynamic strength. However, a more useful way of looking at EMS is its effect on athletic performance – can it lead to improved performance, and is it a viable training option?

Figure 2. Table produced by Seyri & Maffiuletti in their review paper “Effect of Electromyostimulation on Muscle Strength and Sports Performance”

As seen in Figure 2, many studies have proven the efficacy of EMS in improving strength and jumping ability, and in some cases sprinting ability. The longest-running study from this paper was the 2007 study on elite rugby players, which lasted 12 weeks. A test group of 15 players went through two 6-week bouts (first 3 sessions/week, then 1 session/week) of EMS on the plantar flexors, knee extensors, and gluteus muscles, and a control group of 10 players received no training; both groups performed tests at 0, 6, and 12 weeks. The EMS group showed improvements compared to the controls not only in strength (squat, leg extension) but also in power (squat jump and drop jump height), an attribute more translatable to sport performance. The test group, however, saw no power increases after 6 weeks, only 12, and no improvement in sprint times over 12 weeks. The decision to change the training protocols halfway through the experiment does not discredit the results, but makes it more difficult to clearly see the relationship between protocol and result. The study on tennis players, at 4 weeks long, showed large improvements in maximum voluntary contractile force of the quadriceps and small, yet significant, improvements in sprint times and counter-movement jump heights. The study on soccer players, at 5 weeks long, showed the greatest improvements in strength and kicking power (measure by ball velocity) to come between weeks 3 and 5, with no improvements before week 3. It, however, demonstrated EMS to cause no changes to sprint ability.

Figure 3. A professional soccer player exerting force onto a soccer ball

While these studies and many others confirm the ability of EMS intervention to improve strength and in many cases other measures of power that relate to on-field performance, they do not compare EMS directly to a voluntary training program. The rugby study’s control group underwent no additional training, and the tennis and soccer studies had no control groups. They each could have had a group that underwent voluntary strength training in parallel to the other groups. The argument against this, though, is that a voluntary training program requires more time and effort that is in short supply for busy athletes; the tennis study mentioned the virtue of EMS for players with busy competitive schedules who don’t have the time for voluntary strength training. In this regard, it appears that EMS can be used as a tool to enhance athletic performance. However, the most valuable questions right now concern how to incorporate EMS with regular training programs, at different periods of athletes’ competitive schedules, to reap the greatest benefits of sport-applicable muscle function.

Recommended Further Reading

Is high-frequency neuromuscular electrical stimulation a suitable tool for muscle performance improvement in both healthy humans and athletes? (Review)

The Truth About EMS – Electronic Muscle Stimulation: Facts and Fallacies (good explanation of muscle physiology)

Questions to consider:

Have you ever used EMS? Was it for muscle recovery, neuromuscular reeducation, strength training, or as part of a sports-specific training program?

Would you or would you ever have spent $200 to $1000 on an EMS device that could give you an in-season advantage in your particular sport?


Calories and Power in Exercise Equipment



Recommended Reading:

Calculating caloric expenditure with ACSM equations

How the Peloton bike calculates power output (watts)

Lesson plan on bike ergonometry

The accuracy of the ACSM cycle ergonometry equation

Watts calculator for Concept 2 rower

Making sense of calorie-burning claims

Exercise Physiology for Health, Fitness, and Performance


Barbells: Withstanding the 1,000-lb Deadlift


Barbells have been used for strength training for centuries, and the basic design of those used today was invented in 1928, yet they remain one of the most popular and effective exercise tools out there. From the main power lifts of bench, squat, and deadlift, to the olympic lifts of clean, jerk, and snatch, and limitless other movements, a barbell can be used to target any muscle group to improve strength and power. However, it must retain its shape. Through countless loading cycles, years of use, and sometimes extreme bending stresses, a barbell needs to be ready to be picked up and used again right away, and that means it cannot yield, or permanently bend – this would make it more difficult to use, change its motion patterns, and put it at risk of breaking. While typical use of a barbell for most people would not push it to its mechanical limits (Figure 1), those who compete in weightlifting often place so much weight on the ends of the bar that it indeed bends very much (Figure 2).  A barbell must be constructed of the proper material to withstand the loads it is placed under and bend without becoming permanently bent – or, in engineering terms, deform elastically but not plastically.

Figure 1. Use of a loaded barbell to perform a deadlift

Figure 2. Use of an extremely heavily loaded barbell to perform a deadlift


When it comes to competition weightlifting, there are actually different dimensions and specifications required of barbells used for different lifts – read about it here. I decided to focus on a barbell for deadlifting because it’s the movement that can be done with the most weight and is not dynamic like olympic lifts. I borrowed dimensions from the most commonly-used barbell for deadlifting, the Texas 7-1/2″ Bar (Figure 3).

Figure 3. Dimensions of the most commonly-used barbell made for deadlifting

I also decided to design for preventing yield failure rather than fatigue failure because it is a more pressing design concern; it would make more sense to constrain for yielding and optimize for fatigue life rather than the other way around.

The world record deadlift is 500 kg (1,102.3 lbs) by Eddie Hall, so I used a weight of 453.6 kg (1,000 lbs), as events involving more weight than this are so infrequent that yielding in that case would not be of particular concern. This weight is divided into two evenly distributed loads at the ends of the bar, treated as a point load at the center of the distribution, while the opposing forces act where the hands would be placed (I assumed this to be the middle of the knurled portion as seen in Figure 3) [Figure 4].

Figure 4. Lifting of a barbell designed as a beam deflection problem

However, the problem can be simplified to fit a common pattern of loading/support (Figure 5), allowing for a few simple hand calculations to find the stress in the bar. This requires ignoring the weight of the bar itself (which, because of its even distribution and relative lightness, is not crucial anyway) and placing the loads at the very ends of the bar. In the end these assumptions will skew the estimate towards a slightly higher stress, giving an even safer design constraint.

Figure 5. Beam ends overhanging supports & two equal loads applied at symmetrical locations –


By calculating the bar’s moment of inertia, the distance from the neutral axis, and the section modulus of the cross section of the beam, the maximum bending stress can be found to be 587 MPa (Figure 6).

Figure 6. Simplified representation of a loaded, held barbell and calculation of stress

Therefore, the barbell must be made of a material with a yield strength greater than 587 MPa. A look at a plot of materials’ yield strengths shows that metals, ceramics, and composites are all possibilities (Figure 7).

Figure 7. A plot of different materials’ yield strengths compared to their densities (from the text Materials Engineering, Science, Process and Design by Ashby et. al, 2007)

Metals make the most sense, however, because of their density and ductility. Composites’ light weight means they would be difficult, or impossible, to make into regulation-weighted-and-dimensioned barbells. Ceramics are also very brittle, meaning they break before bending at all; it is usually safer for a product to give warning before breaking, in the form of bending, making a ductile metal a better choice. Given its cost compared to titanium alloys, steel is easily the best choice for a barbell.

There is a dizzying amount of different steel mixtures and grades, but based on searching through tables and information sheets such as this and this, it is a safe bet that molybdenum-alloyed steels (steel alloy 4140/4340, yield strength 655/852 MPa) , cold worked austenitic stainless steels (stainless steel grade 301/304/310, yield strength 470-1310 MPa), and martensitic stainless steels (stainless steel grade 410/420/431, yield strength 415-1895 MPa) are all appropriate choices for a barbell that would not suffer permanent deformation even under the most weight a human has ever (dead)lifted.



Get Shredded Easily, As Seen on TV

Patent title: Wheeled Exercise Device

Patent number: US 20120157274 A1

Patent filing date: December 16, 2011

Patent issue date: April 21, 2015

How long it took for this patent to issue: 3 years, 4 months

Inventors: Ian MacColl, Tylor Garland, Jayson Pegler, George Clark, Alden Mills

Assignee: Implus Footcare, LLC (Durham, NC)

US Classification: 482/132

How Many Claims: 10

We’ve all seen them, at least briefly before flipping channels – the exercise equipment infomercials with chiseled models using the latest and greatest workout invention to “tone”, “flatten”, “sculpt”, and “shred” their bodies into perfection. Some are commercial successes that facilitate good workouts, like the Iron Gym … and some are the Shake Weight.  Ab rollers, such as the Perfect Fitness Ab Carver Pro (hereafter referred to as the ACP), tend to fall in the former category.

An ab wheel is an exercise device that, in its most basic form, consists of a wheel with handles on either side. One uses it to strengthen their core (rectus abdominis, internal and external obliques, transverse abdominis, and to a lesser extent, the muscles of the lower back) by kneeling with hands grasping the handles and rolling the wheel forward, maintaining a straight spine as the shoulders move into flexion, and then rolling the wheel back towards the body, bringing the shoulders back in extension. It is a demanding and effective movement for building abdominal strength because of its nature as an anti-extension stability exercise, which strengthens the spine’s ability to resist hyperextension. The basic ab wheel is both effective and ubiquitous, and several variations had already been brought to market; yet, the inventors of the Ab Carver Pro sought to design a unique and superior product.

Figure 1. A general view of the Ab Carver Pro

As it is an improvement upon existing products, the ACP’s claims cannot be separated from comparisons to its predecessors in the art. The most prominent is the Ab Slide, which, encased by plastic housing, has a series of wheels and internal coils that provide a resistive force moving forward and a restoring, or assistive, force moving backward. The problem suggested, though, is that with this and other similar products, either the user is required to hold the handles firmly against the restored turning force, or the restoring force is transmitted through gears that reduce its effectiveness. The ACP claims a mechanism that provides this resistive and restorative force in an optimized way with the internal spring (carbon steel!) attached between an inner surface of the wheel and and the central axle within the interior cavity (Figure 2). There exist interior ribs to prevent coil misalignment.

Figure 2. The internal coil mechanism that provides resistive and restorative forces during exercise

The ACP also claims its “tire overmold” and wide surface, giving it more stability and safety than previous products. The edges of the “tire” are also angled to allow for stable “carving”, or rolling out to either side to engage different muscles to greater intensity (the obliques, as well as the glutes and deltoids, of the side being rolled towards). Rather than the perpendicular, uncontoured handles of its predessecors, the ACP claims its ergonomically designed handles, sloped downward “like a pilot’s steering mechanism” and ending in a slip-preventing ridge. Inventor Alden Mills explains in a video on the product’s website that they did a university study to prove the handle design’s engagement of the triceps muscles, and it showed engagement on the level of a triceps extension, making this not only a core workout but an arm one too. The handle is also designed to reduce stress on the wrists and shoulders.  The patent filed encompasses other versions of the product with bells whistles which are not part of the commercially available product, including one or multiple clutches to engage and disengage different levels of resistance, an electronics module with microchip/microprocessor and LCD display to convey workout data such as distance and repetitions, and a knee pad accessory.

I thought to research this patent because one day I came home from college and the Ab Carver Pro lay on my living room floor (my dad received it free through some rewards-program catalogue).  I did not know about the resistive/restorative coil before I used it for the first time, and I found the feature quite effective. Effective enough, in fact, as to render the device a less effective option for those with moderately to well-developed abdominal strength than a basic ab wheel. Thinking in retrospect, I also did not notice a marked increase in triceps activation and would like to see the claimed “university study” proving this myself. Furthermore, the handle design did not make my wrists and shoulders sing in relief – it simply looked nice and apparently offers a marketing angle. However, it would be worthwhile to gather other people’s opinions on the product, and in its elementary function as an ab wheel, it is a successful product, one that can effectively be used to “tone” and “sculpt” the abdominal muscles as advertised.