Exercise Metabolism

Exercise Metabolism

1. Exercise

   • Planned and structured body movement, which, when repeated (ie: training) results in learning or improving one or more physical skills or in maintaining and improving one or more physical abilities 
   • Physical activity
     • Any bodily movements produced by muscle activity that results in energy expenditure above resting level
   • Exercise parameters
     • 1. Type 2. Intensity 3. Duration/volume 4. Frequency
     • Exercise intensity
       • Often expressed as a % of max intensity (ie. % of 1RM, % HRmax, % VO2max)
       • MET (metabolic equiv. of a task) is a general measure of intensity 
       • 1 MET = O2 uptake at rest which is 3.5 mL x kg x min^-1
       • ex: exercise eliciting O2 uptake of 14 mlxkgxmin^-1 has an intensity of 4 MET
       • RPE is a dimensionless # that one gives when. asked to rate perceived intensity on a scale of 6-20 (Borg)
     • Exercise frequency
       • Exercise is executed once (acute) or repeated on separate days (training)
       • Exercise training is necessary to induce metabolic adaptations 
       • The body modifies its metabolism to meet the requirements of repeated exercise with a reduced disturbance to homeostasis 
     • Exercise duration/volume
       • Duration is classified as short, moderate, or prolonged (subjective)
       • In endurance exercise, the emphasis is on distance covered
       • In resistance training, the emphasis is on the # of reps per set or # of sets

2. Metabolism

   • The sum of biochemical reactions occurring in a living organism 
   • The biochemical reactions involved in converting food to fuel
   • Phases of metabolism
     • Catabolism & anabolism
     • Catabolism
       • The breakdown of complex molecules in living organisms to form simpler ones, together with the release of energy; destructive metabolism.
       • Energy rich substrates carbs, lipids, proteins) -> energy poor-end products (CO2, H2O, NH3)
     • Anabolism
       • The synthesis of complex molecules in living organisms from simpler ones together with the storage of energy; constructive metabolism.
       • Precursor molecules amino acids, hexoses, fatty acids) -> complex molecules (polysaccharides, lipids, nucleic acids, proteins)
   • Amino acids, peptides, & proteins
     • Protein comes from Greek Proteins "first rank"
     • Proteins are built from amino acids - 20 proteinogenic amino acids (incorporated biosynthetically into proteins during translation
     • Protein functions
       • Regulation Signaling Transport Catalysis Movement Structure
     • Protein turnover
       • Synthesis > breakdown =  + net protein balance (anabolism)
       • Breakdown > synthesis = - net protein balance (catabolism)
       • Content of a protein can reflect the use of that protein
     • Amino acid structure
       • Amino acids share same general structure
       • C atom with 4 groups attached via a single covalent bond
       • At physiological pH, the amino and carboxyl group are ionized with positive and negative charge
       • Amino acids are electrically neutral (zwitterion) unless the side chain is charged
     • Charged amino acids
       • Negatively charged amino acids = "acidic" as they are proton donors 
       • Positively charged amino acids = "basic" as they are proton acceptors
     • Stereoisomerism
       • Amino acids can exist in 2 forms: L and D amino acids
       • L and D = mirror images of each other
       • Refers to position of ammonium group (left side = L or levo; right = D or dextro)
       • Humans use L amino acids
     • Peptides
       • Short stretches of amino acids joined together via their carboxyl groups via a peptide bond
       • Peptide bonds form between the C atom of the carboxyl group of one amino acid and the N atom of the amino group of another amino acid
       • Characteristics of peptides
         • Amino acids in a peptide = amino acid residues
         • Peptides have a different prefix based on # of amino acids in peptide (ie: 2 = di, 3 = tri, oligo
         • Amino acid residues designated by 3 letter code (eg: Ser for serine) followed by a number (eg: 473)
         • Ser-473 refers to serine in the 473rd amino acid in the amino acid sequence of the peptide
         • Peptides have a free amino acid and carboxyl group
         • Peptides and proteins are named starting the the free amino group (amino (N)-terminus) and going to the free carboxy group (Carboxyl (C)-terminus)
         • The amino acid at the N-terminus is designated number 1 in the amino acid sequence of a peptide
         • Location of serine, tyrosine, and threonine in a protein is important as these amino acids are phosphorylated, resulting in a phosphoprotein
         • A phosphate group reacts with the -OH group of the side chain of Ser, Thr, or Tyr in an esterification reaction
       • Proteins
         • Longer chain of amino acids = polypeptide
         • Protein structure
           • Primary, secondary, tertiary, quaternary 
           • Primary structure
             • The sequence of amino acids starting from the N-(amino) terminus joined together via peptide bonds
             • "Backbone" of a polypeptide is formed by the alternation of 3 atoms: nitrogen, alpha-carbon, carboxyl-carbon
             • The variable groups (R) protrude from the backbone ('side chains')
           • Secondary structure
             • Refers to the shape of the polypeptide "backbone"
             • The main force responsible for the secondary structure of a protein is the hydrogen bond
             • A hydrogen bond appears between H atom with partial + charge and an atom (usually O or N) with partial - charge
             • 2 common secondary structures = alpha helix and beta pleated sheet
             • Both are stabilized via H-bonds at regular intervals along polypeptide backbone (side chains not considered)
           • Tertiatry structure
             • Refers to conformation of entire polypeptide chain
             • Necessary to confer protein functionality
             • Due to side chain chemical bonds/interactions: H bonds, electrostatic (or ionic). bonds, disulfide bonds, hydrophobic interactions
           • Quaternary structure
             • Refers to proteins composed of more than one polypeptide chains or subunits (dimeric, trimeric, multimeric proteins)
             • Arrangement of entire complex of subunits
           • Bonding & Interactions
             • Hydrogen bonds
               • A hydrogen bond appears between a hydrogen atom with a partial positive charge and an atom (usually O or N) with a partial negative charge
             • Ionic bond (electrostatic)
               • Occurs between oppositely charged groups due to the attraction of opposite charges
               • example: charged carboxylate or ammonium groups
             • Disulfide bond
               • A type of covalent bond that joins 2 cysteine residues resulting in a disulfide (S-S) bond and the loss of 2 H atoms
             • Hydrophobic interaction
               • Side chains of non polar (hydrophobic) amino acids cluster in the interior of a protein molecule due to repulsion from surrounding water
           • Protein denaturation
             • Some of the bonds and interactions that maintain 2ndary, 3rdary, and 4nary are weak so they may be denatured
             • Denaturation refers to the disruption in the overall conformation of a protein (ie. unfolding) with loss of biological activity 
             • Changes in temperature and pH can disrupt protein structure (extreme pH can cause addition or removal H+)
             • Protein denaturation is usually permanent (ie. irreversible) 
         • Enzymes

3. Principles of exercise metabolism

   • Exercise metabolism obeys the need to supply energy for muscle activity 
   • Exercise is always fuelled by a combination of energy sources (not a single source) key sources = carbohydrates + lipids
   • Exercise changes metabolism not only in the active muscles, but also in other organs and tissues
   • Changes in metabolism with exercise depend on exercise parameters, characteristics of the exercising, individual, and environmental factors
   • Metabolism does not return to the characteristics of the resting state immediately after the end of exercise. Many changes persist for hours to days, and others manifest during recovery from exercise rather than during exercise
   • Frequent repetition of exercise (ie. training) can make the metabolism of an individual different from that of an individual who does not train, both at rest and during exercise
   • Many of the metabolic changes elicited by exercise training increase performance and improve health or protect against disease

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