Functions of the lower limb
Function of the lower limb:
● The main function of the lower limb is to support body weight and minimal expenditure of
energy.
● The vertical line through the center of gravity through the legs is slightly posterior to the
hip joints and anterior to the knee and ankle joints and directly over the circular support
base formed by the feet on the ground holding the knee and hip joints in extension
● There is a locking of these joints ( knee area) when standing to reduce muscular energy
required to stand in this position
Function of the lower limb :
● Locomotion : Movements from the hip joints are flexion, extension, abduction, adduction,
medial and lateral rotation, circumduction
● Knee and ankle joints are primarily hinge joints and include movements of dorsiflexion
(movements from the dorsal side of the foot towards the leg) and plantar flexion
● Locomotion of the limb includes pelvic tilt in the coronal plane , pelvic rotation and
transverse plane, movements towards the knees and midline, flexion of the knee and
complex interactions between the hip and the knee.
● Pelvic rotation in the transverse plane minimises the drop in center of gravity by
effectively lengthening the limbs
● Pelvic tilt (Drop) on swing side minimizes rise in center of gravity
Research question 1 (function of the lower limb in supporting body weight)
What are the biomechanical principles that allow the lower limb to support the body weight with
minimal energy expenditure ?
● Postural alignment - proper alignment of the hip, knee and ankle keeps the center of
mass over the base of support reducing muscle effort
● Passive support structure- Ligaments e.g iliofemoral ligament, knee capsule, plantar
fascia provide stability without active muscle use
● Energy- efficient gait : Inverted pendulum mechanism where the legs swing naturally
minimizing energy use.
● Elastic storage - where the Achilles tendon and plantar fascia absorb and release energy
to aid movement
● Joint stability: Where the hips deep socket (acetabulum) enhances passive stability
● The knee knocking mechanism (screw-home mechanism) allows extended standing
minimal muscle effort
● The foot arches distribute weight and absorb shock efficiently
● Efficient muscle use: Eccentric contractions (controlled muscle lengthening) reduce
energy demand
, ● Antigravity muscles (gluteus Maximus, quadriceps, soles) maintain posture it’s minimal
activation
● reflective stability : stretch reflexes and automatic postural adjustments help balance with
minimal effort
How does the position of the body’s center of gravity influence the overall stability and efficiency
of standing posture ?
Influences of center of gravity on standing ability:
● Relationship between the center of gravity and the base of support :
1. Center of gravity within base of support: greater stability requiring minimal muscle effort
(standing upright with feet shoulder width apart, a deep squat, sitting in a chair)
2. Center of gravity near the edge : increased postural sway requiring more muscle
activation to maintain balance (leaning forward or backward on your heels )
● Height of center of gravity
1. Lower center of gravity (bending knees) increases stability by reducing movement
2. Higher center of gravity (standing on tiptoes) reduces stability making balance hard to
maintain
● Postural adjustments :
1. Ankle strategy : small center of gravity shifts are corrected using ankle muscles
2. Hip strategy : larger center of gravity movements require adjustments
3. stepping strategy: if center of gravity moves beyond base of movement a step is needed
to restore balance
Clinical relevance:
Postural alignment disorders : How can abnormalities in the alignment of the body center of
gravity e.g scoliosis affect the efficiency of weight bearing and lead to musculoskeletal
problems?
1. Uneven weight distribution
● scoliosis causes a curve in the spine shifting the center of gravity. This leads to uneven
pressure on the spine, hips and legs . This results in some muscles and joints working
harder than others leading to fatigue and joint pain
2. Joint stress and damage
● misalignment puts uneven pressure on joints like the hips, knees and lower back causing
wear and tear over time. The result of this is a increased risk of arthritis and joint
problems
3. Muscle imbalances
● The body compensates for misalignment by overworking certain muscles e.g one side of
the spine and underusing others. This can result in muscle strain, pain and weakness in
certain areas
4. Poor posture and balance
Function of the lower limb:
● The main function of the lower limb is to support body weight and minimal expenditure of
energy.
● The vertical line through the center of gravity through the legs is slightly posterior to the
hip joints and anterior to the knee and ankle joints and directly over the circular support
base formed by the feet on the ground holding the knee and hip joints in extension
● There is a locking of these joints ( knee area) when standing to reduce muscular energy
required to stand in this position
Function of the lower limb :
● Locomotion : Movements from the hip joints are flexion, extension, abduction, adduction,
medial and lateral rotation, circumduction
● Knee and ankle joints are primarily hinge joints and include movements of dorsiflexion
(movements from the dorsal side of the foot towards the leg) and plantar flexion
● Locomotion of the limb includes pelvic tilt in the coronal plane , pelvic rotation and
transverse plane, movements towards the knees and midline, flexion of the knee and
complex interactions between the hip and the knee.
● Pelvic rotation in the transverse plane minimises the drop in center of gravity by
effectively lengthening the limbs
● Pelvic tilt (Drop) on swing side minimizes rise in center of gravity
Research question 1 (function of the lower limb in supporting body weight)
What are the biomechanical principles that allow the lower limb to support the body weight with
minimal energy expenditure ?
● Postural alignment - proper alignment of the hip, knee and ankle keeps the center of
mass over the base of support reducing muscle effort
● Passive support structure- Ligaments e.g iliofemoral ligament, knee capsule, plantar
fascia provide stability without active muscle use
● Energy- efficient gait : Inverted pendulum mechanism where the legs swing naturally
minimizing energy use.
● Elastic storage - where the Achilles tendon and plantar fascia absorb and release energy
to aid movement
● Joint stability: Where the hips deep socket (acetabulum) enhances passive stability
● The knee knocking mechanism (screw-home mechanism) allows extended standing
minimal muscle effort
● The foot arches distribute weight and absorb shock efficiently
● Efficient muscle use: Eccentric contractions (controlled muscle lengthening) reduce
energy demand
, ● Antigravity muscles (gluteus Maximus, quadriceps, soles) maintain posture it’s minimal
activation
● reflective stability : stretch reflexes and automatic postural adjustments help balance with
minimal effort
How does the position of the body’s center of gravity influence the overall stability and efficiency
of standing posture ?
Influences of center of gravity on standing ability:
● Relationship between the center of gravity and the base of support :
1. Center of gravity within base of support: greater stability requiring minimal muscle effort
(standing upright with feet shoulder width apart, a deep squat, sitting in a chair)
2. Center of gravity near the edge : increased postural sway requiring more muscle
activation to maintain balance (leaning forward or backward on your heels )
● Height of center of gravity
1. Lower center of gravity (bending knees) increases stability by reducing movement
2. Higher center of gravity (standing on tiptoes) reduces stability making balance hard to
maintain
● Postural adjustments :
1. Ankle strategy : small center of gravity shifts are corrected using ankle muscles
2. Hip strategy : larger center of gravity movements require adjustments
3. stepping strategy: if center of gravity moves beyond base of movement a step is needed
to restore balance
Clinical relevance:
Postural alignment disorders : How can abnormalities in the alignment of the body center of
gravity e.g scoliosis affect the efficiency of weight bearing and lead to musculoskeletal
problems?
1. Uneven weight distribution
● scoliosis causes a curve in the spine shifting the center of gravity. This leads to uneven
pressure on the spine, hips and legs . This results in some muscles and joints working
harder than others leading to fatigue and joint pain
2. Joint stress and damage
● misalignment puts uneven pressure on joints like the hips, knees and lower back causing
wear and tear over time. The result of this is a increased risk of arthritis and joint
problems
3. Muscle imbalances
● The body compensates for misalignment by overworking certain muscles e.g one side of
the spine and underusing others. This can result in muscle strain, pain and weakness in
certain areas
4. Poor posture and balance
