Understanding Kinetic Chains in Human Movement
Kinetic Chains in Human Movement
Most everyday gestures require the mobilization of various joints to ensure the movement of different bones relative to each other. This system is called a complex mechanical articulated chain and gives the body the possibility of moving in all planes of space.
All the muscles, not only polyarticular but also monoarticular, act as engines of different links on bone joints, forming the KINETIC CHAIN MUSCLE. The organization of muscle kinetic chains almost always corresponds to reactions of stabilization and equilibration.
Types of Kinetic Chains
There are three main types of kinetic chains:
- Open Kinetic Chain: Characterized by a fixed proximal end and a free distal end that moves.
- Closed Kinetic Chain: The distal end is fixed, and the proximal end moves.
- Braked Kinetic Chain: A chain whose distal external resistance is less than 15% of the maximum resistance is considered an open or slightly braked chain. When the resistance is greater than 15%, the chain is considered closed or severely hampered.
Muscle Action in an Open Kinetic Chain
Analysis of a Kinetic Unit
A kinetic unit consists of three elements: two bone links, a joint, and a muscle motor system.
Consider a joint with one degree of mobility, allowing flexion and extension. Two muscle groups are involved:
- Agonists: Muscles performing the primary movement (e.g., biceps brachii, brachialis, and brachioradialis in elbow flexion).
- Antagonists: Muscles opposing the primary movement (e.g., triceps brachii and anconeus in elbow flexion).
In joints with multiple degrees of freedom, like the shoulder, muscle roles can change depending on the movement plane. For example, the anterior deltoid acts as a synergist in shoulder flexion but an antagonist in movements occurring in the frontal plane.
Analysis of an Open Kinetic Chain
In shoulder flexion, the pectoralis major, anterior deltoid, and coracobrachialis work together. For this to function correctly, the shoulder girdle muscles (upper trapezius, levator scapulae, lower trapezius, serratus anterior, and others) contract to stabilize the scapula. As flexion occurs, the shoulder girdle adjusts to extend the displacement.
Open kinetic chains, or slightly braked chains, are primarily used for:
- Speed: Mobilizing one link accelerates the next, increasing distal speed (ballistic movement).
- Accuracy: Stabilizing the proximal link is crucial for accurate distal movement. Co-contraction of agonists and antagonists may occur for slow, precise control.
The recruitment of synergistic muscles in an open chain is always near-distal. This is important when designing exercises for weak muscles in a distal open kinetic chain.
Muscle Action in a Closed Kinetic Chain
Analysis of a Closed Kinetic Unit
A closed kinetic unit is similar to an open unit, but the direction of muscle force is reversed. The distal end of the muscle is considered fixed, and the proximal attachment is the motive force.
Analysis of a Closed Chain
Muscle action becomes more complex when considering multiple joints. Two examples illustrate this:
- Triple Extension of the Lower Extremity: Muscles like the triceps surae, soleus, gastrocnemius, hamstrings, hip extensors, and quadriceps work together to extend the hip, knee, and ankle joints.
- Lombard’s Paradox: Describes the coactivation of the hamstrings (hip extensors and knee flexors) and the rectus femoris (hip flexor and knee extensor) during triple extension. This occurs because of the different lever arm lengths at the hip and knee joints.
Closed kinetic chains prioritize strength and economy. The recruitment of synergistic muscles in a closed chain is generally distal-proximal. This recruitment pattern is beneficial for strengthening weak proximal muscles.
Series and Parallel Chains
Beyond open and closed chains, muscle associations can be further categorized as series or parallel chains.
Series Chain
In a series chain, all skeletal muscles involved in the movement are located on the same side of the joint axes. All bone links move in the same direction, as in kicking a ball.
- Speed: The curvilinear trajectory of the distal end results from the summation of angular displacements at each joint, leading to high distal speed.
- Force: Resistance applied at the distal end creates increasing resistance moments at each joint proximally. Proximal muscles are highly solicited, while distal muscles can only generate low force due to the high resistance moments.
Parallel Chain
In a parallel chain, synergistic muscles are positioned alternately on either side of the joint axes. Bone segments move in opposite directions, as in the triple extension of the leg when climbing stairs.
- Strength: This arrangement favors force production due to the shorter lever arms and the alternating muscle actions.
- Stability: The alternating muscle contractions provide stability and reduce the risk of bone injury from bending forces.
Series and parallel chains can coexist within the same movement. For example, a shot putter utilizes a parallel chain in the lower extremities for support and a series chain in the trunk and upper extremity for throwing.
Mode of Recruitment
Muscle recruitment can occur in two ways:
- Proximal-to-Distal: Contraction starts proximally and progresses distally, as in throwing a ball.
- Distal-to-Proximal: Contraction originates distally and progresses proximally, as in pulling oneself up on a bar.
The mode of recruitment is independent of the type of chain. Both series and parallel chains can be recruited either proximally or distally.
Summary
, motor organization includes several notions:
1 .- The string type muscle in which muscle activity falls (serial or
in parallel).
2 .- The mode of recruitment used (proximodistal or distoproximal).
The phenomenon of stabilization or equilibration associated with this organization and motor
can complete the analysis.
The mode of recruitment is independent of the type of organization in driving and chains
series and parallel can be recruited indiscriminately as a form proximodistal
or disto-proximally.