Sports Medicine & Physiology: Energy Systems, Rehab & VO2 Max

For physiotherapy entrance exams (AIIMS, Jamia) and sports physio practice, understanding the physiology behind performance and specific athlete rehabilitation protocols is essential. This guide covers the metabolic pathways, nutritional strategies, and advanced rehab protocols.

1. Energy Systems

The body uses adenosine triphosphate (ATP) as currency. The method of generating ATP depends on the Intensity and Duration of the activity.

System	Fuel Source	Duration	Example Sport
ATP-PC (Phosphagen)	Stored ATP & Creatine Phosphate	0 - 10 seconds (Max Intensity)	100m Sprint, Powerlifting, High Jump
Anaerobic Glycolytic (Lactic Acid)	Muscle Glycogen (No Oxygen)	10 sec - 2 mins (High Intensity)	400m Run, 200m Swim
Aerobic (Oxidative)	Glycogen & Fats (Requires Oxygen)	> 2 mins (Low to Moderate Intensity)	Marathon, Distance Cycling

2. Sports Nutrition Strategies

A. Carbohydrate Loading (Glycogen Supercompensation)

Used by endurance athletes to maximize muscle glycogen stores before a major event.

• Protocol: Taper training (reduce intensity) 3-4 days before the event while increasing Carbohydrate intake (8-10g per kg of body weight).
• Benefit: Delays onset of fatigue (hitting the wall).

B. Hydration

• Dehydration Rule: A loss of body water equal to 2% of body mass significantly impairs performance.
• Post-Event Rehydration: Drink 1.5 liters of fluid for every 1 kg of body weight lost during exercise.

3. Sports Injury Rehabilitation Protocols

A. Tennis Elbow (Lateral Epicondylitis)

• Pathology: Microtrauma at the origin of Extensor Carpi Radialis Brevis (ECRB).
• Management: Eccentric strengthening of wrist extensors (Tyler Twist), Bracing (counterforce brace), and scapular stabilization.

B. Rotator Cuff Rehab (Post-Op/Conservative)

Focus is usually on the Supraspinatus tendon.

1. Phase 1 (Protection): 0-4 weeks. Sling use. Pendulum exercises. Passive ROM (avoid active abduction).
2. Phase 2 (Motion): 4-8 weeks. Active Assisted ROM (cane exercises). Isometrics.
3. Phase 3 (Strengthening): 8-12 weeks. Theraband exercises (Internal/External Rotation). "Full Can" exercise (Scaption) minimizes impingement compared to "Empty Can".
4. Phase 4 (Return to Sport): >12 weeks. Plyometrics, throwing drills.

[Image of rotator cuff rehabilitation exercises]

C. Meniscus Repair Rehab (Athlete Specific)

Unlike a meniscectomy (removal), a repair requires protection of the healing sutures.

• Restriction 1: Weight-bearing is often limited (NWB or PWB) for 4-6 weeks (especially for radial tears).
• Restriction 2: No Knee Flexion > 90° for 4 weeks (deep flexion compresses the posterior horn of the meniscus).
• Restriction 3: Avoid open kinetic chain (OKC) resisted hamstrings exercises early on (hamstring tendon attaches to meniscus).

4. Plyometrics & Agility

Mechanism: Plyometrics utilize the Stretch-Shortening Cycle (SSC). A rapid eccentric stretch (loading) is immediately followed by a concentric contraction (explosive release).

• Examples: Box Jumps, Depth Jumps, Hops.
• Criteria to start: Athlete should be able to Squat 1.5x their body weight (classic guideline) and have full pain-free ROM.
• Agility Drills: Ladder drills, T-Test, Illinois Agility Test (Tests change of direction speed).

5. VO2 Max & METs Calculation

VO2 Max (Maximum Oxygen Consumption)

• The gold standard measure of cardiorespiratory fitness.
• Fick Equation: VO2 Max = Cardiac Output (Q) × (a-vO2 difference).
• Resting Value: 3.5 ml/kg/min (This is 1 MET).
• Elite Value: >70-80 ml/kg/min.

METs (Metabolic Equivalent of Task)

Used to estimate the energy cost of physical activity.

Formula: 1 MET = 3.5 ml O2 / kg / min.

Example Calculation:
If an activity requires 35 ml/kg/min of oxygen, what is the MET level?
Answer: 35 / 3.5 = 10 METs (Vigorous activity).

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Frequently Asked Questions (FAQs)

Q1: Which muscle is most commonly involved in Tennis Elbow?

The Extensor Carpi Radialis Brevis (ECRB) is the primary muscle involved, specifically at its origin on the lateral epicondyle.

Q2: Why is deep squatting avoided after Meniscus Repair?

Deep flexion (bending >90 degrees) places high shear and compressive forces on the posterior horn of the meniscus, which can tear the fragile sutures during the healing phase.

Q3: What is the difference between "Empty Can" and "Full Can" exercises?

Both target the Supraspinatus. However, the "Empty Can" (thumb down) causes shoulder impingement. The "Full Can" (thumb up) activates the muscle equally well but with significantly less risk of impingement, making it the preferred rehab exercise.

Exam Quiz: Sports Medicine (10 MCQs)

Test your knowledge. Click the correct option to see the answer and reasoning.

1. Which energy system is the primary source of ATP for a 100m sprint (approx. 10 seconds)?

Correct Answer: A
The ATP-PC (Phosphagen) system provides immediate energy for high-intensity, short-duration activities lasting up to 10 seconds.

2. One Metabolic Equivalent (1 MET) is equal to how much oxygen consumption?

Correct Answer: B
1 MET represents the resting metabolic rate, which is standardly defined as 3.5 ml of Oxygen per kg of body weight per minute.

3. In Plyometrics, the "Stretch-Shortening Cycle" involves a rapid _______ contraction followed by an explosive concentric contraction.

Correct Answer: C
The muscle must first lengthen (eccentric loading) to store elastic energy, which is then released during the concentric phase.

4. Which exercise is considered safest and effective for Supraspinatus strengthening?

Correct Answer: B
The "Full Can" exercise (thumb up) in the scapular plane avoids subacromial impingement while effectively isolating the Supraspinatus.

5. A performance decrement is typically observed when dehydration levels reach what percentage of body weight loss?

Correct Answer: B
Losing 2% or more of body weight due to fluid loss increases heart rate and body temperature, leading to a decline in physical and mental performance.

6. Following a Meniscus Repair, knee flexion is usually restricted to _______ for the first 4 weeks.

Correct Answer: C
Flexion beyond 90 degrees increases posterior shear stress on the meniscus, risking the integrity of the surgical repair.

7. Carbohydrate loading is most beneficial for which type of athlete?

Correct Answer: D
Carb loading maximizes glycogen stores, which is critical for endurance events lasting longer than 90 minutes where glycogen depletion is the limiting factor.

8. The "Fick Equation" determines VO2 Max by multiplying Cardiac Output (Q) by:

Correct Answer: A
VO2 Max = Q × (a-vO2 diff). This represents the ability of the heart to pump blood (Q) and the muscles' ability to extract oxygen (a-vO2 diff).

9. In the treatment of Lateral Epicondylitis (Tennis Elbow), which type of exercise has the strongest evidence for pain relief?

Correct Answer: C
Eccentric loading of the wrist extensors (e.g., using a FlexBar or dumbbell) helps remodel the collagen structure of the tendinopathic ECRB.

10. An athlete performing at 10 METs is working at what level of intensity?

Correct Answer: C
Activities <3 METs are light, 3-6 METs are moderate, and >6 METs are considered vigorous. 10 METs indicates high-intensity effort.

References

1. Brukner, P., & Khan, K. (2017). Clinical Sports Medicine. McGraw-Hill Education.
2. McArdle, W. D., Katch, F. I., & Katch, V. L. (2010). Exercise Physiology: Nutrition, Energy, and Human Performance. Lippincott Williams & Wilkins.
3. Ellenbecker, T. S., & Cools, A. (2010). Rehabilitation of the Rotator Cuff. Current Reviews in Musculoskeletal Medicine.