ACSM-EP Musculoskeletal Anatomy — Questions and Answers
Question 1: During the ascent phase of a barbell back squat, which muscle is the primary hip extensor?
- Iliopsoas
- Gluteus maximus (Correct answer)
- Tibialis anterior
- Rectus abdominis
Correct answer: Gluteus maximus
The gluteus maximus is the primary hip extensor and drives the hips upward out of the squat bottom position.
The gluteus maximus is the prime mover for hip extension, working with the hamstrings and quadriceps (knee extension) during the squat ascent. The iliopsoas is a hip flexor and would oppose, not drive, hip extension. The tibialis anterior dorsiflexes the ankle and the rectus abdominis flexes the trunk, so neither produces the main upward force. Knowing prime movers helps an exercise physiologist select exercises and cue clients correctly.
Question 2: A client performs a lat pulldown, pulling the bar from overhead down to the upper chest. Which shoulder joint action is the latissimus dorsi producing?
- Flexion and horizontal adduction
- Abduction and external rotation
- Adduction and extension (Correct answer)
- Elevation and upward rotation
Correct answer: Adduction and extension
Pulling the arms from overhead down toward the body is shoulder adduction and extension, the main actions of the latissimus dorsi.
Moving the humerus from an overhead position down toward the trunk combines adduction in the frontal plane with extension in the sagittal plane, which are the primary actions of the latissimus dorsi (with the teres major and posterior deltoid assisting). Flexion with horizontal adduction describes a pushing or chest-fly motion driven by the pectoralis major and anterior deltoid. Abduction with external rotation and scapular elevation with upward rotation describe overhead raising motions, the opposite of the pulldown.
Question 3: Which of the following muscles is NOT part of the rotator cuff group?
- Supraspinatus
- Infraspinatus
- Subscapularis
- Deltoid (Correct answer)
Correct answer: Deltoid
The deltoid is a large superficial shoulder muscle and is not one of the four rotator cuff (SITS) muscles.
The rotator cuff consists of the supraspinatus, infraspinatus, teres minor, and subscapularis (SITS), which stabilize the humeral head in the glenoid fossa. The deltoid is a superficial prime mover for shoulder abduction, flexion, and extension but does not belong to the cuff. Rotator cuff weakness or imbalance is a common cause of shoulder impingement, so exercise professionals should recognize these muscles when designing shoulder programs.
Question 4: The hamstring muscles (biceps femoris, semitendinosus, semimembranosus) cross both the hip and knee. Which combination of actions do they produce?
- Knee flexion and hip extension (Correct answer)
- Knee extension and hip flexion
- Knee flexion and hip flexion
- Knee extension and hip extension
Correct answer: Knee flexion and hip extension
Because they cross behind both joints, the hamstrings flex the knee and extend the hip.
The hamstrings originate on the ischial tuberosity and insert on the tibia or fibula, passing posterior to both the hip and the knee. This produces knee flexion and hip extension. Knee extension and hip flexion describe the rectus femoris, which crosses in front of both joints. Understanding two-joint muscles explains why exercises like Romanian deadlifts and leg curls both train the hamstrings.
Question 5: Which muscle pair is primarily responsible for ankle plantar flexion during a standing calf raise?
- Tibialis anterior and extensor digitorum longus
- Gastrocnemius and soleus (Correct answer)
- Peroneus tertius and tibialis anterior
- Popliteus and plantaris
Correct answer: Gastrocnemius and soleus
The gastrocnemius and soleus form the triceps surae, the primary plantar flexors via the Achilles tendon.
The gastrocnemius (most active with the knee extended) and the soleus (more active with the knee bent) together make up the triceps surae and insert through the Achilles tendon on the calcaneus. The tibialis anterior and extensor digitorum longus are dorsiflexors on the front of the shin. Popliteus and plantaris are minor contributors. Performing both standing and seated calf raises targets each muscle more effectively.
Question 6: According to Wolff's law, which type of exercise is most effective for stimulating increased bone mineral density?
- Swimming
- Seated cycling
- Weight-bearing and resistance exercise (Correct answer)
- Water aerobics
Correct answer: Weight-bearing and resistance exercise
Bone remodels in response to mechanical loading, so weight-bearing and resistance exercise best stimulate bone density.
Wolff's law states that bone adapts to the mechanical stresses placed upon it, increasing density where loading occurs. Impact activities and resistance training provide osteogenic stimulus at the hip and spine. Swimming, seated cycling, and water aerobics are low-impact or buoyancy-supported and provide little skeletal loading. ACSM recommends weight-bearing aerobic activity and resistance training to help maintain bone health and reduce osteoporosis risk.
