Workout physics: Forces and Torques in Muscles and Joints

Muscles, bones & joints are an interesting application of force statics. Human muscles exert way more than we can think of. Muscular fibers generate the tension by actin & myosin cross-bridge ( myosin is the motor protein that plays a major role in muscle contraction. While actin is the spherical protein that forms filament, that plays a role in muscle contraction & different cellular processes) cycling. As you work out in your workout clothes your body experiences tension, during that muscle may elongate, contract shortens, or attain the same length. Different types of muscle contractions happen when your body undergoes a moment that is defined by a change in muscular length during the contraction. Though this term contraction relates to shortening, while referring to the muscular system, this means tension generation in the muscle fiber.


Biomechanics is defined as the movement science of the living body. It explains how our muscles, tendons, bones, ligaments, and joints complement each other in producing the movement. It specifically focuses on the mechanics of human movements. The circulation of fluids, reaction to the physical stress and tension, and other body moments comes under its umbrella. The refresh and finding of this field are very beneficial in yielding the best of your workouts. Following are the elements of biomechanics:

  • Dynamics: It is the study of biological systems that come in motion with acceleration & deceleration
  • Kinematics: It describes the forces and their effects on a human system in biomechanics. It includes motion patterns such as linear & angular changes of velocity with time and position as well.
  • Kinetics: In biomechanics, It is the study of causes of motion, forces, & moments when your muscles work
  • Statics: In biomechanics, it is the study of systems that come in equilibrium, or work at a constant rate and energy.

Muscular Contractions

Following are the types of muscular contraction that occur in the human body, no matter if you are working out in your workout clothes, performing athletic training, or simply doing everyday chores, these moments are responsible for your physical actions.

  • Isotonic Contractions: These types of contractions maintain a constant tension in your muscle as it changes its length. Isotonic contractions can either be eccentric or concentric.
  • Concentric Contraction: Concentric contraction is the type of muscular contraction during which body muscles reduce in length and generate force and overcome resistance. This type of contraction usually occurs during heavy weight lifting. The concentric contraction in your biceps causes the bending of your arm at the elbow.
  • Eccentric Contractions: This type of contraction results in your muscle elongation while your muscle still generates the force. In this case, the resistance your muscle faces is way greater than the force generated. This type of contraction can be voluntary & involuntary. (Voluntary eccentric-contraction involves the controlled lowering of the heavyweight that you have raised, Involuntary eccentric-contraction occurs when the weight is way too much for your muscles to bear. Your muscles constantly remain in tension in this type of contraction.
  • Isometric Contractions: Opposite to the isotonic contractions, the isometric contraction in your muscles generates the force without any change in their length. Commonly the muscles of your hand & forearms undergo this contraction type. They are used for maintaining posture. This type of contraction is also described as yielding and overcoming.
  • Yielding: This contraction occurs when the muscle contraction in the human body is opposed by an outer resistance. Such as holding the heavyweights steady, without any movement. Overcoming: This type of contraction occurs when the muscle contraction in your body is recessed by some immovable object like the contraction generated in your muscles while you are pushing a wall.

Force & velocity of muscular contraction

A number of factors change by the force that is developed in your muscle cells. A direct relationship exists between the length of your muscles and the development of isometric force.

As your muscle length increases, an active force developed in your muscles reaches it’s maximum & decreases. At the upper extreme your heart functions properly. The force of your heart muscles also depends on the frequency at which a particular muscle is being stimulated. With the increase of stimulus frequency the force increases until it reaches it’s maximum, then it starts declining. The increase in circulation of epinephrine & norepinephrine from sympathetic-nervous systems increases contraction force. All the factors combined help the heart in developing high required force required. At the given contraction velocity.

The cardiovascular demands vary from situation to situation. As you begin to move your cardiac output tends to increase. It also increases when your heart pumps against high pressure. These stressful conditions require adjustments. Exercising is a short-term increase in demand. It is met by boosting the force & contraction frequency.

Smooth muscle

The smooth muscles are found in the outer covering of almost all hollow organs found in the human body. The functioning of your cardiovascular, gastrointestinal, respiratory, & reproductive systems largely depended on the constrictive motions of the smooth cells. The smooth muscles vary from striated muscles, as its name implies, the smooth muscle found in the uniform appearance lacks obvious striping features that striated muscles have. The contraction capability of smooth muscle is 50% less of fast skeletal muscles but is generated by comparable 300 times lower chemical energy. The difference in the amount plays a great role in the altered mechanical properties of both muscles.

Torque in the human body

Torque is the phenomenon that creates movement in the joints of the human body. It is highly important to understand that torque is the prime process of creating movements in the lever system. Maximizing the torque a muscle is capable of generating allows the strengthening of that particular muscle in the human body. Higher the amount of torque produced by a muscle, greater movement in it capable of producing under the action of applied force or tension. If the main goal is increasing the moment of range, in that case, the torque can be varied for maximizing the muscular efficiency that is required for moving the body. One of the main examples of torque is the barbell biceps curl workout. Moving the bar is a lot harder when you fully extend your elbows compared to the position in which they are at an angle of 90°. 

Angle-torque relationships are mainly responsible for this phenomenon.

As of this relation, greater torque is produced when the applied force makes an angle of 90 degrees with the lever. This concept should be kept in mind for the opposite goal. By altering the application angle of the moment arm, the components of the force vector can be changed for maximizing the compressive force. An increase of compressive force on the muscles is usually the goal when you want to maximize the body’s stability.

Rotator cuffs can be used for demonstrating these types of vector forces vectors where muscles synergistically contract for creating the compressive forces couple so that the humeral head can be stabilized in the glenoid fossa. While you are trying to alter the amount of torque, make sure you realize that your joint’s ROM doesn’t necessarily correlate with the torque your muscle is creating. Your angle of insertion does not depend on your joint’s ROM. These muscles cross those joints which have different insertions. For determining force vectors on a muscle, evaluate the line of pull in that relationship on the lever of your arms & joint axis. The most usual examples of this effect can be seen in the patella’s effect.

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