Anatomy and physiology of EMS training
Functional components of a striated muscle fiber
- The striated muscles make up about 40% of the body weight.
- Functions: Support and holding function as well as movement (together with tendons, bones and joints).
- Depending on its size, the muscle consists of several muscle bundles (fascicles).
- The fascicles are made up of several muscle fibers.
- The muscle fiber represents the muscle cell.
- The striation of a muscle fiber results from the regular arrangement of the contractile proteins actin and myosin.
- The myofibrils are divided into approximately 2 μm long sarcomeres by Z-stripes.
- The sarcomere is the smallest contractile unit of a muscle.
- The sarcolemma is the cell membrane that surrounds the muscle fiber and extends into the tendons.
Contraction mechanism – sliding filament mechanism
- Myosin head attaches to G-actin (cross-bridge formation) because the myosin binding site is exposed by calcium.
- Myosin head tilts from a 90° to a 45° position – shortening of the sarcomere.
- The myosin head is separated from the actin by an ATP molecule and “pre-tensioned” like a spring.
- ATP is split into ADP and Pi by ATPase.
- The cycle begins again.
Main fiber types of skeletal muscle
Type I: Slow, red fiber type (ST fibers, slow twitch fibers)
- Slow contraction time, approx. 80 ms.
- Higher myoglobin content, rich in capillaries and mitochondria.
- Predominantly aerobic/oxidative metabolism.
- Low ATPase activity.
- For endurance work, e.g. supporting muscles.
- They are activated first during classical exercise (before FT fibers).
- Can be optimally controlled via EMS with up to 30 Hz.
Type II: Fast, white fiber type (FT fibers, Fast Twitch Fibers)
- Short contraction time, approx. 30 ms.
- Divided into oxidative-glycolytic (type 2a) and glycolytic (type 2x) fibers.
- Predominantly anaerobic metabolism.
- High ATPase activity.
- For fast movements.
- Easily electrically excitable due to low stimulation threshold of the motor neurons.
- Can be optimally controlled via EMS between 50 and 100 Hz.
- During EMS training, it can also be activated before the ST fibers become tired.
Energy supply
- The breakdown of ATP to ADP is the basis for every muscle contraction.
- Aerobic metabolism: CO₂ and H₂O are produced in the mitochondria.
- Anaerobic metabolism: Glycogenolysis outside the mitochondria – lactate is produced, which leads to intracellular acidification and reduces performance.
Sore muscles
weakness
- Damage to the Z-disks within the myofibrils.
- Osmotic effects lead to water retention in the muscle.
- Increase in CK levels as an indication of muscle damage.
- Creatine kinase (CK) is excreted in the urine via the kidneys.
Pains
- Degradation of destroyed substances leads to pain-causing substances (e.g. histamine).
- Reflexive tension increases the pain.
- Drink plenty of water to avoid muscle soreness and major damage, especially during EMS training, as many muscle groups are trained simultaneously.
Transmission of stimuli from nerve cells to muscle fibers
- The starting point of the contraction process is the coupling of the electrical nerve impulses to the mechanical contraction.
- Motor neurons start in the anterior horn cells of the spinal cord.
- The totality of muscle fibers innervated by a motor neuron is called a motor unit.
- The excitation is transmitted via the motor end plate.
Resting potential
Every cell has a resting potential (approximately 60–100 mV in muscle and nerve cells). The cell interior is negatively charged, the cell exterior is positively charged. The resting electrical potential is caused by an uneven distribution of ions (potassium, sodium, and chloride).
Conclusion
The red type I endurance muscles are best trained with EMS at a frequency of up to 30 Hertz. These muscles are used in cardio training and have a more athletic effect.
Fast-twitch, large-area white skeletal muscles of type II are best trained at a frequency of 50 to 100 hertz. These muscles appear bulkier and are activated during intense exercise.
