Unit 2: Body Systems & Their Role in Exercise
Musculoskeletal
  • Muscles, Tendons, Ligaments, Bones
Cardiovascular
  • Heart, Arteries, Veins, Blood
Respiratory
  • Nose, Mouth, Lungs, Alveoli
Guiding Questions:
  • What role do our body systems play in our wellness?
  • How is muscle built/lost?
  • Why does this matter?
The Musculoskeletal System & Exercise
Understanding how our bodies move and adapt to physical activity is the foundation for effective exercise!
  • Role: This system includes the bones, muscles, tendons, and ligaments that form the structural framework for the body and enable movement.
  • In Exercise: Skeletal muscles contract to produce movement for activities like running, jumping, and lifting. Bones adapt to mechanical stress by building more dense tissue.
What is the Musculoskeletal System?
Our body's movement framework consists of several key components working in harmony:
  • Muscles that contract to generate force and movement
  • Bones that provide structure and leverage
  • Tendons that connect muscles to bones
  • Ligaments that connect bones to other bones
Beyond movement, this system maintains posture and protects vital organs!
Muscle Contraction Types: Concentric vs. Eccentric
Concentric Contraction
Muscle shortens while generating force
Example: The upward phase of a squat
Powers acceleration and lifting movements
Eccentric Contraction
Muscle lengthens while under tension
Example: The downward phase when lowering a weight with control
Creates greater muscle tension and microtears that stimulate growth
Effective exercise programs incorporate both types for optimal muscle development and functional strength.
Brain Break: Feel the Force!
Let's take a quick break to physically experience concentric and eccentric muscle contractions in action. Stand up and follow along!
The Lift (Concentric)
Slowly lift your arm as if doing a bicep curl. Feel your bicep muscle shorten as you bring your hand towards your shoulder.
The Lower (Eccentric)
Now, slowly lower your arm back down with control. Notice how your bicep muscle lengthens under tension as it resists the movement.
Repeat a few times, focusing on the feeling of your muscles working in both phases. Great job!
The Sliding Filament Theory: How Muscles Contract
Structure
Muscle fibers contain thousands of sarcomeres with interlocking actin (thin) and myosin (thick) protein filaments
Activation
Nerve signals trigger calcium release, exposing binding sites on actin filaments
Contraction
Myosin heads attach to actin, pull, detach and reset in a rowing motion, powered by ATP energy
Result
Filaments slide past each other, shortening the sarcomere and creating muscle contraction
3-2-1- Action!
Hypertrophy: Building Muscle Mass
Regular resistance exercise triggers a cascade of adaptations that lead to increased muscle size:
  • Microscopic damage to muscle fibers stimulates repair and growth
  • Increased protein synthesis builds new contractile proteins
  • Progressive overload drives continued adaptation
These changes result in stronger muscles that improve performance and health.
Atrophy: Muscle Loss from Inactivity
The Process
Without regular stimulus, muscle protein breakdown exceeds synthesis, causing fibers to shrink
Begins within 72 hours of inactivity
Can reduce muscle mass by 3-5% per week during complete immobilization
The Impact
Decreased strength and power
Reduced metabolic rate and energy expenditure
Compromised functional independence, especially in older adults
Bone and Joint Adaptations to Exercise
1
Bone Remodeling
Weight-bearing activities stimulate osteoblasts (bone-building cells) to increase bone mineral density and strength
2
Joint Health
Exercise strengthens supporting structures, enhancing joint stability and function
3
Connective Tissue
Tendons and ligaments become stronger and more resilient with proper training
Musculoskeletal Health & Aging
Age-Related Changes
  • Sarcopenia: 3-8% muscle mass loss per decade after age 30
  • Reduced bone density and increased fracture risk
  • Decreased tendon elasticity and joint flexibility
Exercise Benefits for Aging Adults
  • Preserves muscle mass and functional strength
  • Improves balance & coordination - reducing fall risk
  • Enhances quality of life and independence
Practical Exercise Tips for Musculoskeletal Health
Resistance Training
Include 2-3 sessions weekly targeting major muscle groups
Focus on proper form with both concentric and eccentric phases
Weight-Bearing Cardio
Incorporate walking, jogging, or stair climbing for bone health
Aim for 150+ minutes of moderate activity weekly
Flexibility & Mobility
Include dynamic stretching before and static stretching after exercise
Maintain joint mobility with full range of motion exercises

Safety First: Consult healthcare professionals before beginning a new exercise program, especially with pre-existing conditions. Proper progression is key to preventing injury.
Summary: The Power of Movement
The musculoskeletal system is remarkably adaptable, responding to the demands we place upon it throughout our lives.
Understand
Knowledge of muscle actions and adaptations optimizes training effectiveness and injury prevention
Consistency
Regular exercise preserves strength, mobility and metabolic health across the lifespan
Action
Every movement counts—start today to build a stronger, more resilient musculoskeletal system
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