Function and Dysfunction of Hamstrings

Transcription

1 Function and Dysfunction of Hamstrings A. Hamstrings Function 1. Eccentrically decelerate the thigh and lower the leg during swing phase. (last 20% of swing phase) 2. Concentrically assist in extending the hip while improving knee stability. (18% to 28% of stance phase) 3. Provide antagonistic force to ipsilateral hip flexors for pelvic stability. (40% to 58% of initial swing phase) 4. Provide force absorption of the body weight during early stance. 5. Protect the knee from hyperextension during single leg stance or standing through co-activation with quadriceps. This co-contraction leads to posterior translation of the tibia and its tuberosity and allows concomitant flexion of the patella. 6. Responsible for reciprocal gait: a. Produces knee flexion at initial swing. b. Stabilizes pelvis with contralateral hamstring during mid swing. Maximum concentric contraction occurs here. c. Control knee extension, tibial external rotation and re-extend the hip at late swing. 7. Bicep femoris (ER) becomes a stabilizer for femoral acetabular internal rotators (anterior gluteus medius, gluteus minimus, tensor fascia latae, ischiocondylar adductor magnus, semimembranosus and semitendinosus). 8. Semimembranosus and semitendinosus (IR) become stabilizers for femoral acetabular external rotators (iliopsoas, gluteus maximus, piriformis, gemelli, obturators, proximal adductor magnus, and biceps femoris). B. Hamstring Dysfunction Occurs: 1. when they become too long (> 110 SLR) 2. when there is insufficient strength laterally or improper muscle alignment of corresponding femoral acetabular external rotators. Consequently, the bicep femoris becomes more active (tone) as a femoral acetabular external rotator and ineffective as an acetabular femoral (pelvic) stabilizer or pelvic external rotator. Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 1

2 3. when there is insufficient strength medially or improper muscle alignment of corresponding femoral acetabular internal rotators. Consequently, the semitendinosus and semimembranosus become more active femoral acetabular internal rotators and ineffective as acetabular femoral (pelvic) stabilizers or internal rotators. 4. when plantar flexors (gastrocnemius and soleus) become overused, strong and tight. Limited dorsiflexion during gait results in decreased hip extension at mid and end stance phase. Hamstring function (as stabilizers and FA/AF rotators) is compromised and overuse of quadriceps, piriformis, tensor fascia latae and iliopsoas increases. 5. when the anterior capsule of the hip (iliofemoral and pubefemoral ligaments) is overstretched. In other words, hamstring dysfunction occurs when the force couple in a sagittal plane is lost. C. Hamstring Strain and Ruptures The literature mentions several factors associated with hamstring muscle strain. They include flexibility, strength, hamstring/quadriceps strength ratio, eccentric muscle contraction, fatigue, adverse neural tension, and improper warm up. However, very little research reflects the relationship between hamstring strains and strength of gluteals, FA rotators, and adductors (including contralateral and ipsilateral). Muscles with a high percentage of type II (fast twitch) fibers are more likely to be injured because of the implications of faster contraction of muscle. Hamstrings are primarily composed of fast twitch fiber. No research can be found to support the suggestion that fast twitch fibers, in a muscle that is in a long resting state, takes on slow twitch fiber characteristics. 1. Bicep Femoris (ER) strains occur on the ipsilateral side of an anteriorly rotated hemi-pelvis. This pelvic position results in delayed hip extension during early heel strike or late swing phase. Excessive demands are placed on the lengthened hamstring as it attempts to eccentrically control internal rotation. These strains can also occur contralateral to the side of the anteriorly rotated hemi-pelvis secondary to concomitant femoral internal rotation. (see case example) 2. Semitendinosus (IR), Semimembranosus (IR), and Adductor Magnus (IR) strains occur on the ipsilateral side of an anteriorly rotated hemi-pelvis. This is secondary to the medial hamstrings acting as an antagonist to an overactive psoas that concomitantly externally rotates the femur during midstance, terminal swing, and preswing. These individuals usually have an overly stretched anterior capsule (Ober test is positive, modified Thomas is negative and you can hear a click when testing hip extension). Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 2

3 3. Examination Considerations: a. How much FA internal and external rotation do they have? Strength? b. Can they adduct their lower extremities on a stable pelvis? c. Can they extend their femur without extending their back? d. Do they have equal strength upon resisted knee flexion in sitting with the femur positioned internally in the acetabulum and with the femur positioned externally in the acetabulum? e. When does strain occur? When did the pull occur? f. Is it a bicep femoris or a semi issue? 4. Intervention a. Reposition pelvis if appropriate through hamstring activation on the appropriate side. b. Determine status of anterior acetabular femoral capsule. If stretched or lax you will need to increase IR strength from gluteus medius and long muscle of the adductor magnus; not the tensor fascia latae. c. Retest FA PROM and AROM, FA adduction and extension. d. Design a home exercise program: For the bicep femoris strain (a femoral external rotator and a pelvic extensor). 1. Restore position 2. Maintain hamstring activity 3. Strengthen gluteus maximus 4. Strengthen external rotation concurrently with hamstring activity and gluteus maximus activity (prone) 5. Possibly need to strengthen internal rotators with seated reciprocal activity to maintain neutral pelvic position. For the Semitendinosus/Semimembranosus (femoral internal rotators, hip extensors, and adductors) 1. Restore position 2. Maintain hamstring activity 3. Strengthen gluteus medius 4. Strengthen internal rotation concurrently with hamstring activity and adductor activity. 5. Possibly need to strengthen external rotators with seated reciprocal activity to maintain neutral pelvic position. 6. Strengthen adductors in open chain (2 weeks after initiation of program) Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 3

4 D. Case Study Example 21-year-old runner has pulled his hamstring running the 400m dash, eleven times over the last 3 years. Objective Findings: Passive Values with Gross Strength Left FA IR 42 5/5 FA ER 43 5/5 SLR 95 Full FA adduction Full FA extension Adductors 5/5 Right FA IR 68 3+/5 FA ER 65 3+/5 SLR 95 Full FA adduction Full FA extension Adductors 5/5 Strength Values Left glute max 5/5 glute med 5/5 med HS 5/5 lat HS 5/5 Right glute max 3+/5 glute med 4-/5 med HS 4-/5 lat HS 3+/5 Assessment: Pelvic alignment and position is neutral. Femoral acetabulum rotation measurement and weakness reflects possible insecurity of R hip compared to the L. Appears to be overusing bicep femoris for FA ER. He will need more FA/AF stability and control in general or will probably strain his lateral hamstring again. His medial hamstring is protected and not strained even though weak, because neighboring adduction strength is good. He needs to increase R proximal FA ER first to decrease ER demands on bicep femoris. Recommendations: 1. Strengthen R glute max as an external rotator while actively extending hip (sidelying or prone). 2. Strengthen R glute med as an external rotator (posterior fiber) in sidelying. Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 4

5 3. Strengthen adductors with active internal rotation or external rotation. stand on R LE, pull L LE in toward middle simultaneously while turning L foot in, with tubing on L ankle for R adduction with AF IR and FA ER demands on R. stand on L LE, pull R LE in toward middle simultaneously turning R foot in with tubing on R ankle for adduction with FA IR demands on R. Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 5

6 4. Stand on a 4 to 6 inch block with R LE. Lower, rotate, and cross L LE in front of the R LE, while keeping R femoral acetabular joint stable. Control acetabular femoral IR on R by going slow when L LE in front of R. Bring L LE back up to neutral and to top of block without moving R femur. Repeat. Add 5 lbs to L ankle for more R AF ER demand. 5. Run clockwise around a track intentionally pushing off with L LE to increase L IR open chain demands and L ER closed chain demands. Copyright May 2001 Postural Restoration Institute. All Rights Reserved. 6