Week 7 Module 7: Muscle Maladaptation

Maladaptation in Skeletal Muscle to Inactivity

• Maladaptation is the opposite of adaptation, occurring during inactivity or disuse of skeletal muscle.
• Physical inactivity can stem from physical injuries, illnesses, aging, or lifestyle choices.
• Spaceflight leads to unloading of mechanical stress on skeletal muscle, resulting in loss of muscle and bone mass.
• Astronauts must exercise for 2.5 hours daily to mitigate unloading effects on muscles.

Consequences of Inactivity

• Muscle atrophy frequently occurs due to muscle disuse.
• Muscle wasting impacts health by impairing metabolic and endocrine functions.
• Bed rest and immobilization lead to unloading; spaceflight is a major unloading factor.
• Unilateral lower limb suspension mimics inactivity from spaceflight and shows physiological maladaptations including:
  • Decreased maximum force and rate of force development.
  • Reduced tendon stiffness and contractile components.
  • Impaired force steadiness, crucial for tasks requiring fine motor skills (steady force reduction reported at ~22% and 12% for knee extensors and plantar flexors).
  • Muscular endurance declines by ~13% and ~24% after 21 and 30 days of inactivity respectively.
  • Decreased VO2peak and ventilatory threshold levels.
  • Whole muscle size reduces at 2.5% per week for knee extensors, more for plantar flexors.
  • Shift to fast-twitch muscle fibers enhances explosiveness but increases fatigability.
  • Muscle composition alters: intramuscular fat increases, along with reduced enzyme activity for oxidative phosphorylation.
  • Increased reliance on anaerobic glycolysis observed, raising fatigue susceptibility.
  • Loss of bone density occurs, which exercise alone cannot offset.
  • Decreased neural conduction velocity and increased presynaptic inhibition lead to reduced muscle activation.

Mechanisms of Maladaptation due to Inactivity/Unloading

• Changes in the nervous system critically affect muscle function.
• Impairments in the central nervous system (CNS) reduce muscle contraction signals despite unaffected motor unit activation.
• Delays in nerve conduction velocity and increased presynaptic inhibition result from inactivity.
• Electrical activity in muscles, as measured by electromyography (EMG), decreases, indicating reduced capacity for muscle activation and potential atrophy.
• Alterations in muscle protein synthesis and breakdown lead to muscle loss; decreased protein synthesis rates combined with increased protein degradation rates contribute to muscle atrophy.

Maladaptation in Skeletal Muscle to Inactivity

• Maladaptation is the opposite of adaptation, occurring during inactivity or disuse of skeletal muscle.
• Physical inactivity can stem from physical injuries, illnesses, aging, or lifestyle choices.
• Spaceflight leads to unloading of mechanical stress on skeletal muscle, resulting in loss of muscle and bone mass.
• Astronauts must exercise for 2.5 hours daily to mitigate unloading effects on muscles.

Consequences of Inactivity

• Muscle atrophy frequently occurs due to muscle disuse.
• Muscle wasting impacts health by impairing metabolic and endocrine functions.
• Bed rest and immobilization lead to unloading; spaceflight is a major unloading factor.
• Unilateral lower limb suspension mimics inactivity from spaceflight and shows physiological maladaptations including:
  • Decreased maximum force and rate of force development.
  • Reduced tendon stiffness and contractile components.
  • Impaired force steadiness, crucial for tasks requiring fine motor skills (steady force reduction reported at ~22% and 12% for knee extensors and plantar flexors).
  • Muscular endurance declines by ~13% and ~24% after 21 and 30 days of inactivity respectively.
  • Decreased VO2peak and ventilatory threshold levels.
  • Whole muscle size reduces at 2.5% per week for knee extensors, more for plantar flexors.
  • Shift to fast-twitch muscle fibers enhances explosiveness but increases fatigability.
  • Muscle composition alters: intramuscular fat increases, along with reduced enzyme activity for oxidative phosphorylation.
  • Increased reliance on anaerobic glycolysis observed, raising fatigue susceptibility.
  • Loss of bone density occurs, which exercise alone cannot offset.
  • Decreased neural conduction velocity and increased presynaptic inhibition lead to reduced muscle activation.

Mechanisms of Maladaptation due to Inactivity/Unloading

• Changes in the nervous system critically affect muscle function.
• Impairments in the central nervous system (CNS) reduce muscle contraction signals despite unaffected motor unit activation.
• Delays in nerve conduction velocity and increased presynaptic inhibition result from inactivity.
• Electrical activity in muscles, as measured by electromyography (EMG), decreases, indicating reduced capacity for muscle activation and potential atrophy.
• Alterations in muscle protein synthesis and breakdown lead to muscle loss; decreased protein synthesis rates combined with increased protein degradation rates contribute to muscle atrophy.

Maladaptation in Skeletal Muscle to Inactivity

• Maladaptation is the opposite of adaptation, occurring during inactivity or disuse of skeletal muscle.
• Physical inactivity can stem from physical injuries, illnesses, aging, or lifestyle choices.
• Spaceflight leads to unloading of mechanical stress on skeletal muscle, resulting in loss of muscle and bone mass.
• Astronauts must exercise for 2.5 hours daily to mitigate unloading effects on muscles.

Consequences of Inactivity

• Muscle atrophy frequently occurs due to muscle disuse.
• Muscle wasting impacts health by impairing metabolic and endocrine functions.
• Bed rest and immobilization lead to unloading; spaceflight is a major unloading factor.
• Unilateral lower limb suspension mimics inactivity from spaceflight and shows physiological maladaptations including:
  • Decreased maximum force and rate of force development.
  • Reduced tendon stiffness and contractile components.
  • Impaired force steadiness, crucial for tasks requiring fine motor skills (steady force reduction reported at ~22% and 12% for knee extensors and plantar flexors).
  • Muscular endurance declines by ~13% and ~24% after 21 and 30 days of inactivity respectively.
  • Decreased VO2peak and ventilatory threshold levels.
  • Whole muscle size reduces at 2.5% per week for knee extensors, more for plantar flexors.
  • Shift to fast-twitch muscle fibers enhances explosiveness but increases fatigability.
  • Muscle composition alters: intramuscular fat increases, along with reduced enzyme activity for oxidative phosphorylation.
  • Increased reliance on anaerobic glycolysis observed, raising fatigue susceptibility.
  • Loss of bone density occurs, which exercise alone cannot offset.
  • Decreased neural conduction velocity and increased presynaptic inhibition lead to reduced muscle activation.

Mechanisms of Maladaptation due to Inactivity/Unloading

• Changes in the nervous system critically affect muscle function.
• Impairments in the central nervous system (CNS) reduce muscle contraction signals despite unaffected motor unit activation.
• Delays in nerve conduction velocity and increased presynaptic inhibition result from inactivity.
• Electrical activity in muscles, as measured by electromyography (EMG), decreases, indicating reduced capacity for muscle activation and potential atrophy.
• Alterations in muscle protein synthesis and breakdown lead to muscle loss; decreased protein synthesis rates combined with increased protein degradation rates contribute to muscle atrophy.

Explore the concept of maladaptation in skeletal muscle due to inactivity. This quiz will cover the negative effects of prolonged disuse on muscle function and metabolism. Understand how physical inactivity can lead to significant changes in muscle characteristics.