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Examine the image series.
1. When a muscle "appears" it is physiologically/electrically active
2. The timing of these muscle activities are based on an overall summary created from data contained within the references linked below
3. Individual muscle functions are indicated by different color shadings
4. Muscle functions will be assigned based on:
++++a. Timing of activity-
++++++++i. Maximum or increasing force on hindpaw?
++++++++ii. Swing or decreasing force on hindpaw?
++++b. Muscle attachments
++++++++i. Limb to body?
++++++++ii. Limb to limb?
++++c. Effect of ... or... LACK of effect of... an active muscle on a neighboring joint
5. This module is focused on the walking dog. Trotting and running dogs are discussed in the manuscripts below
JOINT STABILIZING, ANTIGRAVITY AND PROPULSION MUSCLE FUNCTION:
1. Attachments are limb to limb
2. Active during early, mid and the first half of late STANCE, timing correlated with peak forces on pelvic limb
3. Distal attachments are the SHORT END of levers
4. Generate an upward force on the short end of the lever
5. Generate a corresponding downward force on the opposite long side of the lever
6. WHEN THE LIMB IS BEARING WEIGHT this downward force is redirected upwards against an immovable barrier and counters downward gravitational forces
7. Muscles that fulfill the above characteristics and would be considered to have joint stabilizer/antigravity/propulsion functions include:
++++a. Middle gluteal- stabilizes hip joint
++++b. Vastus lateralis, Rectus femoris - stabilizes stifle joint
++++c. Gastrocnemius - stabilizes tarsal joints
8. IN CONTRAST TO THE THORACIC LIMB, when active these muscles do exert "predictable" effects on neighboring joints even though the pelvic limb is bearing weight
++++a. Note extension of the hip, stifle and tarsal joints during early, mid and the beginning of late stance
++++++++i. Middle gluteal- stabilizes and EXTENDS hip joint
++++++++ii. Vastus lateralis, Rectus femoris - stabilizes and EXTENDS stifle joint
++++++++iii. Gastrocnemius - stabilizes and EXTENDS tarsal joints
++++b. Whereas the thoracic limb functions as a "pole vault" during stance, the pelvic limb supplies propulsion. The extension caused by these muscles during weight-bearing in the pelvic limb supplies these forward-propulsive forces. The degree of forward movement (walk versus run) is determined by the extent of activation of these muscles
++++c. Of the muscles listed above the quadriceps femoris muscles supply the MOST propulsive forces
9. Reflect on the example of you standing versus walking on your toes. Your quads, gastrocnemius and gluteal muscles would be acting with stabilizing functions while you stand and stabilizing + propulsive functions when you move forward
10. Pelvic limb muscles with joint stabilizing, antigravity, propulsive functions are shaded light-green in the image series
PRIME MOVER MUSCLE FUNCTION:
1. Attachments are limb to limb
2. Active during the last part of STANCE and SWING, timing correlated with reduced or no forces on the limb
3. Distal attachments are the short end or long end of levers
4. Prime movers shorten when activated and move neighboring joints in traditional, predictable ways
5. Muscles that fulfill the above characteristics and would be considered to have PRIME MOVER functions include:
++++a. Tensor fasciae latae - early swing, late stance, flexes the hip joint
++++b. Sartorius - early/mid-swing, late stance, flexes the hip joint
++++c. Gracilis - early swing, late stance, flexes stifle joint
++++d. Cranial tibial - early swing, flexes tarsal joints
++++e. Iliopsoas - mid-swing, late stance, flexes the hip joint
6. Reflect on the example of contracting your tibialis anterior muscle with your foot off the ground and observing talocrural joint flexion. This would be a prime mover function of the tibialis anterior
7. The primary function of all of these prime movers in concert would be:
++++a. Elevate the limb during swing in preparation for protraction to occur without dragging this distal limb across the ground
++++b. Initiate flexion at the end of stance during a period of force reduction on the hindpaw
8. Muscles with PRIME MOVER functions are shaded RED in the image series
JOINT STABILIZER ANTAGONIST MUSCLE FUNCTION:
1. Attachments are limb to limb
2. Activity correlated with peak forces on limb
3. Distal attachments are the LONG end of levers
4. The opposite side of joints affected by joint stabilizer/antigravity/propulsive muscles
5. Help regulate/control joint stabilizer/antigravity//propulsive muscle function
6. Muscles that fulfill the above characteristics and would be considered to have joint stabilizer antagonist functions include:
++++a. Biceps femoris - helps regulate quadriceps femoris (semimembranosus and semitendinosus have similar activity patterns and function, not shown in image series)
++++b. Iliopsoas - helps regulate gluteal muscles
7. When active these muscles usually do NOT significantly shorten nor exert "predictable" effects on neighboring joints
8. Again, reflect on the example of you walking on your toes. The gastrocnemius muscle would be acting with stabilizing/propulsive functions while the tibialis anterior is functioning as a joint stabilizer antagonist.
9. Muscles with joint stabilizing, antigravity functions are shaded light-blue in the image series
PELVIC LIMB PROTRACTION
1. In contrast to thoracic limb, pelvic limb protraction and retraction is not as clear
2. Attachments are limb to CRANIAL body
3. Active during SWING
4. The muscle that fulfills the above characteristics and would be considered to have PELVIC LIMB PROTRACTION functions include:
++++a. Iliopsoas- when active appears to help rotate the hip bone in a cranioventral direction
5. Muscles with LIMB PROTRACTION functions are shaded purple in the image series
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