Benefits of Physical Activity & Human Energy Systems

Physical Benefits of Regular Physical Activity

• Lower risk of chronic diseases (e.g., cardiovascular disease, type-2 diabetes, certain cancers)
• Improved metabolic efficiency
  • Faster basal metabolic rate → more calories burned at rest
  • Better regulation of blood-glucose and insulin sensitivity
• Strengthens the immune system
  • Increased circulation of immune cells (NK-cells, T-cells)
  • Reduced systemic inflammation
• Helps reduce or maintain healthy body weight
  • Balances caloric intake vs. expenditure
  • Preserves or increases lean muscle mass
• Reduces the risk of premature death
  • Epidemiological data link ≥150 min of moderate activity per week to ≈25 % lower all-cause mortality

Mental & Emotional Benefits of Physical Activity

• Produces a relaxation response → easier onset of deep, restorative sleep
• Reduces symptoms of depression and anxiety
  • Exercise = non-pharmacological treatment, comparable effect size to SSRIs for mild–moderate depression
• Elevates circulating endorphins (the body’s “feel-good” hormones)
  • $\text{Exercise} \; \uparrow \text{Endorphin} \Rightarrow \downarrow \text{Perceived pain} + \uparrow \text{Mood}$
• Enhances cognitive performance & stress resilience
  • Neurogenesis in hippocampus
  • Improved executive function (prefrontal cortex activation)

Defining Energy

• Everyday definition: “Total power & ability to be mentally and physically active.”
• Scientific perspective (in exercise physiology):
  • Capacity to perform work, measured in $\text{Joules (J)}$ or $\text{kilocalories (kcal)}$
  • Comes from breaking molecular bonds in nutrients → captured as chemical energy in ATP.

Energy in the Human Body

• Food → Digestion → Absorption → Cellular metabolism → ATP
• Macronutrients
  • Carbohydrates (CHO)
  • Fats (lipids)
  • Proteins (amino acids)
• Key molecule: Adenosine Triphosphate (ATP)
  • Structure: Adenine + Ribose + 3 Phosphate groups
  • Reaction: ATP \rightarrow ADP + P_i + \text{Energy (≈7.3 kcal·mol^{-1})}
  • Limited intramuscular stores (~80–100 g) ⇒ constant resynthesis required.

Overview of the Three Energy Systems

• Purpose: Resupply ATP at the rate demanded by working muscles.
• Systems operate simultaneously; dominance depends on intensity & duration.

1. Anaerobic A-Lactic System (ATP–CP or Phosphagen System)

• No oxygen required (anaerobic) & no lactic acid produced (a-lactic).
• Fuel: Stored ATP + Creatine Phosphate (CP)
• Dominant for high-intensity, very short activities (≤10 s)
  • Examples: 100 m sprint, maximal vertical jump, 1-RM weight-lifting attempt
• Characteristics
  • Fastest rate of ATP resynthesis (≈2.5 mol ATP·kg dm^{−1}·min^{−1})
  • Very limited capacity (depletes within seconds)
  • Recovery: CP resynthesized aerobically in ≈2–3 min of rest.

2. Anaerobic Lactic System (Glycolytic System)

• Anaerobic: operates without oxygen; produces lactate + H^+ (cause of acidosis-related fatigue)
• Primary fuel: Muscle glycogen / blood glucose
• Dominates during medium–high intensity efforts lasting ≈10 s – 2 min
  • Examples: 400 m run, 50 m swim, repeated ice-hockey shifts
• Characteristics
  • Moderate ATP production rate (≈1.3 mol ATP·kg dm^{−1}·min^{−1})
  • Capacity limited by lactate & proton accumulation
  • Training adaptations: ↑buffering capacity, ↑lactate clearance, ↑glycolytic enzyme activity.

3. Aerobic (Oxidative) Energy System

• Requires oxygen; occurs in mitochondria
• Fuels: Carbohydrates, fats (primary during prolonged/low intensity), and proteins (minimal contribution)
• Dominant during low–moderate intensity activities lasting ≥2 min to several hours
  • Examples: marathon running, cycling tour, brisk walking
• Characteristics
  • Slowest ATP production rate (≈0.8 mol ATP·kg dm^{−1}·min^{−1})
  • Largest capacity (theoretically unlimited with adequate fuel & O_2)
  • By-products: $CO<em>2 + H</em>2O$ (non-fatiguing; expelled via respiration & sweat)
  • Adaptations: ↑mitochondrial density, ↑capillarization, ↑VO_2 max

Interplay & Practical Importance of Energy Systems

• Transition
  • At exercise onset, ATP–CP is engaged first; glycolysis ramps up; oxidative phosphorylation catches up after ≈2 min.
• Training program design should match system demands
  • Sprinters: emphasize ATP–CP power & capacity drills
  • Team-sport athletes: include glycolytic intervals & aerobic base work
  • Endurance athletes: focus on aerobic efficiency, with periodic anaerobic work for speed.
• Health relevance
  • Well-developed aerobic system improves cardiovascular health.
  • Anaerobic conditioning enhances insulin sensitivity & musculoskeletal strength.

Example: Creating an Exercise Routine Based on One System (Class Project Prompt)

• Step 1 – Choose a system (e.g., Anaerobic Lactic)
• Step 2 – List suitable activities:
  • 200 m rowing sprints
  • 30 s cycling at 90 % max effort
  • Battle-rope slams 45 s
  • Shuttle runs 15–20 s
• Step 3 – Organize into a routine (sample):
  1. Warm-up: 5 min light jog + dynamic stretching
  2. Main set (repeat ×4):
  • 30 s cycling sprint
  • 90 s rest
  • 45 s battle-rope
  • 90 s rest
  1. Cool-down: 5 min slow pedaling + static stretching
• Evaluation Criteria (per rubric):
  • Appropriateness 20 pts
  • Attainability 20 pts
  • Group cooperation 10 pts
  • Total 50 pts

Ethical & Practical Considerations

• Always screen participants (PAR-Q) before high-intensity training.
• Gradually progress intensity to minimize injury risk.
• Ensure adequate recovery, hydration, and nutrition (especially CHO availability for glycolytic work).
• Inclusive programming: adapt modalities for different fitness levels & limitations.

Numerical & Biochemical Quick Reference

• Energy yield per substrate (aerobic):
  • $1 \text{mol Glucose} \rightarrow 36–38 \text{mol ATP}$
  • $1 \text{mol Palmitic acid} \rightarrow 129 \text{mol ATP}$
• CP store: ≈80–100 mmol·kg^{−1} dry muscle
• Resting metabolic rate (RMR): ≈3.5 \text{mL O_2·kg^{−1}·min^{−1}} (1 MET)
• Lactate threshold typically at 50–60 % VO_2 max in untrained; ≥80 % in elite endurance athletes.