First off, electromyography (EMG) is a technique employed in measuring electrical activity induced by neural stimulation of skeletal muscle. Two primary versions of EMG are typically used: surface EMG and intramuscular EMG. Surface EMG refers to the use of electrodes being placed on the surface of the skin to measure translated electrical activity from muscular contraction. While convenient, surface EMG can be quite inaccurate due to interference by subcutaneous adipose tissue and translated electrical activity from adjacent muscles. Intramuscular EMG usually involves the direct insertion of a needle electrode into a particular muscle belly. Intramuscular EMG can be sensitive enough to distinguish between the electrical activity of individual muscle fibers but is not immune to electrical artifact. A related technique, termed nerve conduction study (NCS), is occasionally employed in tandem with EMG in order to quantify the conduction of electrical impulses through nerve tissue (such as a nerve which innervates the muscle being looked at through EMG).
EMG data is perhaps most commonly utilized in the field of exercise prescription in attempting to discern which muscles are "activated" to the greatest extent during the performance of a particular movement. While this kind of information can obviously be beneficial, far too many conclusions are typically drawn in a far too absolute manner. Personal trainers, strength and conditioning coaches, and physical therapists often make the mistake of viewing EMG data for a particular movement, and then assuming that a nearly identical pattern of "muscle activation" will be universally exhibited by anyone performing the same movement. There are many problems with such an assumption and I'll briefly outline them here.
Firstly, it is often thought that skeletal muscles do not produce any electrical activity in a state of rest. This is a false thought in that every cell in the human body produces pulses of electromagnetic activity in a fairly continuous fashion, and many factors are capable of altering a cell's pattern of vibrational exhibition (such as diet, psychological stress, infections, etc.). Secondly, while electrical impulses are largely conducted along nerve tissue, nerves are housed within the body's matrices of connective tissue (such as fascial matrices and extracellular matrices). The health and architectural shape and positioning of these connective tissues play a significant role in determining the conductance of electrical impulses through nerves to muscles. For example, the pH level, hydration level, presence of toxic material, and physical architecture of extracellular matrices can and do impact the quantity and pattern of neural stimulation which reaches individual muscle fibers. The values for such variables would obviously vary between individuals and affect the results obtained from any kind of EMG measurement.
Thirdly, analyzing EMG data from an absolute perspective obviously ignores the gamut of motor programming that has been instilled within the nervous system of the individual being measured. Asking someone to perform a particular movement, collecting EMG measurements, and then assuming that an identical pattern of motor recruitment will be exhibited by anyone else performing the same movement is, quite frankly, imbecilic. Certainly some kind of resemblance will likely be seen, but the nervous system does not recruit individual muscles in a universally consistent fashion in order for a particular movement to be performed, it recruits an already established motor pattern which it believes to most accurately mirror the intended movement (infantile motor development would obviously be an exception). Accordingly, one's coordination and array of motor programming would certainly impact the pattern of muscle recruitment during the performance of any movement. Therefore, motor recruitment patterns obviously may not be identical between individuals.
Lastly, because it is related to interpreting EMG data, I feel it needs to be noted that muscles do not pull on bones as is typically believed, they pull on the fascial matrix in which they are embedded, this pulling is then translated to the fascial matrix surrounding bone tissue (this is why there are no true levers within the human body). I already alluded to this earlier, but anything that can alter the biochemical or mechanical operation of the fascial matrices (such as acidity, inflammation, dehydration, chronic tension, nutrient deficiencies, toxin presence, infection (bacterial, fungal, or parasitic), electromagnetic pollution, etc.) can absolutely affect the conductance of electrical impulses through the body and, thus, the pattern of muscle recruitment employed during the performance of any exercise. Long story short, just because some self-proclaimed "fitness expert" tells you that a particular exercise is the best exercise for developing a particular muscle, that doesn't mean it's true or accurate. Article Source
EMG data is perhaps most commonly utilized in the field of exercise prescription in attempting to discern which muscles are "activated" to the greatest extent during the performance of a particular movement. While this kind of information can obviously be beneficial, far too many conclusions are typically drawn in a far too absolute manner. Personal trainers, strength and conditioning coaches, and physical therapists often make the mistake of viewing EMG data for a particular movement, and then assuming that a nearly identical pattern of "muscle activation" will be universally exhibited by anyone performing the same movement. There are many problems with such an assumption and I'll briefly outline them here.
Firstly, it is often thought that skeletal muscles do not produce any electrical activity in a state of rest. This is a false thought in that every cell in the human body produces pulses of electromagnetic activity in a fairly continuous fashion, and many factors are capable of altering a cell's pattern of vibrational exhibition (such as diet, psychological stress, infections, etc.). Secondly, while electrical impulses are largely conducted along nerve tissue, nerves are housed within the body's matrices of connective tissue (such as fascial matrices and extracellular matrices). The health and architectural shape and positioning of these connective tissues play a significant role in determining the conductance of electrical impulses through nerves to muscles. For example, the pH level, hydration level, presence of toxic material, and physical architecture of extracellular matrices can and do impact the quantity and pattern of neural stimulation which reaches individual muscle fibers. The values for such variables would obviously vary between individuals and affect the results obtained from any kind of EMG measurement.
Thirdly, analyzing EMG data from an absolute perspective obviously ignores the gamut of motor programming that has been instilled within the nervous system of the individual being measured. Asking someone to perform a particular movement, collecting EMG measurements, and then assuming that an identical pattern of motor recruitment will be exhibited by anyone else performing the same movement is, quite frankly, imbecilic. Certainly some kind of resemblance will likely be seen, but the nervous system does not recruit individual muscles in a universally consistent fashion in order for a particular movement to be performed, it recruits an already established motor pattern which it believes to most accurately mirror the intended movement (infantile motor development would obviously be an exception). Accordingly, one's coordination and array of motor programming would certainly impact the pattern of muscle recruitment during the performance of any movement. Therefore, motor recruitment patterns obviously may not be identical between individuals.
Lastly, because it is related to interpreting EMG data, I feel it needs to be noted that muscles do not pull on bones as is typically believed, they pull on the fascial matrix in which they are embedded, this pulling is then translated to the fascial matrix surrounding bone tissue (this is why there are no true levers within the human body). I already alluded to this earlier, but anything that can alter the biochemical or mechanical operation of the fascial matrices (such as acidity, inflammation, dehydration, chronic tension, nutrient deficiencies, toxin presence, infection (bacterial, fungal, or parasitic), electromagnetic pollution, etc.) can absolutely affect the conductance of electrical impulses through the body and, thus, the pattern of muscle recruitment employed during the performance of any exercise. Long story short, just because some self-proclaimed "fitness expert" tells you that a particular exercise is the best exercise for developing a particular muscle, that doesn't mean it's true or accurate. Article Source