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Related Concept Videos

Phase I Reactions: Hydrolytic Reactions01:15

Phase I Reactions: Hydrolytic Reactions

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Hydrolysis, a cornerstone of phase I biotransformation reactions, uses water to cleave chemical bonds. This process is pivotal in drug metabolism, generating more polar metabolites that can be easily excreted.
An important hydrolytic reaction is ester hydrolysis. Ester bonds, often found in prodrugs, are broken down, increasing the solubility of drugs like aspirin and lidocaine for more straightforward elimination. Amide hydrolysis is another critical reaction, targeting amide bonds prevalent...
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Phase II Reactions: Acetylation Reactions01:24

Phase II Reactions: Acetylation Reactions

797
Acetylation, a phase II biotransformation reaction, introduces an acetyl group to drugs or their metabolites. Acetyltransferase enzymes facilitate this reaction, which resembles α-amino acid conjugation due to the addition of a functional group to the drug molecule.
The substrates for acetylation are typically drugs or their metabolites with an amino, sulfonamide, or hydrazine functional group. Acetylation can occur at several points in the drug molecule, including primary, secondary, and...
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Phase I Reactions: Reductive Reactions01:27

Phase I Reactions: Reductive Reactions

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Phase I biotransformation reductive reactions are chemical processes that modify drugs by introducing or revealing polar functional groups via reduction. Enzymes called reductases catalyze these reactions, playing a pivotal role in drug metabolism by transforming lipophilic drugs into more polar, water-soluble metabolites for easy excretion. An essential type of reductive reaction is the carbonyl group reduction, where aldehydes and ketones are reduced to alcohols. An example is the...
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Phase II Reactions: Methylation Reactions01:17

Phase II Reactions: Methylation Reactions

701
Methylation is a phase II biotransformation process involving the attachment of a methyl group to a substrate. Enzymes known as methyltransferases orchestrate this reaction.
The mechanism of methylation unfolds in two stages. The first stage sees a methyltransferase enzyme facilitating the transfer of a methyl group from S-adenosylmethionine (SAM) to the substrate, forming S-adenosylhomocysteine (SAH). The second stage involves further metabolism of SAH into homocysteine, which can be recycled...
701
Phase II Reactions: Miscellaneous Conjugation Reactions01:19

Phase II Reactions: Miscellaneous Conjugation Reactions

364
Phase II biotransformations are detoxification mechanisms that conjugate xenobiotics with endogenous substances, neutralizing their toxicity.
A key example involves the conjugation of cyanide ions, which impair cellular respiration and alter hemoglobin into non-oxygen-carrying cyanmethemoglobin. To neutralize this threat, a sulfur atom from thiosulphate is transferred to the cyanide ion, catalyzed by the enzyme rhodanese, resulting in an inactive compound called thiocyanate. The production of...
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Phase II Reactions: Glucuronidation01:24

Phase II Reactions: Glucuronidation

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Glucuronidation, a pivotal phase II biotransformation process, involves the coupling of glucuronic acid to a drug or xenobiotic. Given its widespread occurrence and critical role in drug metabolism, it's considered the most crucial phase II reaction. It enhances the water solubility of substances, aiding their expulsion from the body. The driving force behind these reactions is a group of enzymes known as UDP-glucuronosyltransferases (UGTs). UGTs facilitate the transfer of a glucuronic acid...
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Related Experiment Video

Updated: Jan 26, 2026

Kinematics and Ground Reaction Force Determination: A Demonstration Quantifying Locomotor Abilities of Young Adult, Middle-aged, and Geriatric Rats
10:28

Kinematics and Ground Reaction Force Determination: A Demonstration Quantifying Locomotor Abilities of Young Adult, Middle-aged, and Geriatric Rats

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Running ground reaction force complexity at the initial stance phase increased with ageing.

Shuqi Zhang1,2, Yumeng Li3, Li Li4

  • 1College of Human Movement Science, Beijing Sport University, Beijing, China.

Sports Biomechanics
|April 4, 2019
PubMed
Summary

Older runners show more complex ground reaction forces (GRF) during running, indicating potential changes in muscle coordination with age, though GRF amplitude remains similar across age groups.

Keywords:
Loading ratenonlinear analysisoveruse injurysample entropystability

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Area of Science:

  • Biomechanics
  • Gerontology
  • Sports Science

Background:

  • Ageing can affect musculoskeletal health and running mechanics.
  • The impact of footwear on ground reaction forces (GRF) in older runners is not well understood.

Purpose of the Study:

  • To investigate the effects of age and shoe type on GRF amplitude and complexity in runners.
  • To analyze how ageing influences running biomechanics.

Main Methods:

  • Collected GRF data from 20 healthy runners (13 younger, 7 older) at 3.5 m/s on an instrumented treadmill.
  • Calculated maximal loading rate, GRF variables, and sample entropy of GRF during the initial stance phase.

Main Results:

  • Neither age nor shoe type significantly altered maximal loading rate or GRF amplitude.
  • Older runners displayed significantly higher anteroposterior and vertical GRF sample entropy than younger runners.

Conclusions:

  • Running GRF amplitudes are maintained in older runners, suggesting adequate muscle strength for running demands.
  • Increased GRF complexity with ageing may reflect diminished muscle contraction coordination and force production smoothness.