Unbiased gene expression analysis of 30,000 genes in human skeletal muscle biopsies reveals that the top 30 downregulated pathways in fatigued older adults are all mitochondrial-linked.
"you look at the 30,000 genes in the in the skeletal muscle and you ask in an unbiased way, what are the top 30 pathways that are downregulated? They are all mitochondrial-linked." (said at 0:15:25)
Transcriptomic profiling of human skeletal muscle biopsies across aging, pre-frailty, and sarcopenia consistently shows significant downregulation of mitochondrial genes and oxidative phosphorylation pathways. For example, observational microarray analyses comparing pre-frail older adults to active older adults demonstrated marked downregulation of mitochondrial gene expression alongside impaired respiratory complex activity. While bioenergetic and mitochondrial pathways are among the most prominently enriched downregulated sets in aged muscle, transcriptional remodeling in skeletal muscle aging also involves broader processes including proteostasis, inflammatory signaling, and structural components.
Mitochondrial function in individuals with diabetes is approximately half that of the normal population.
"when you look at mitochondrial function in diabetics, it's like half of the normal population. GUEST1: Half." (said at 0:20:05)
Classic cross-sectional biopsy studies examining skeletal muscle bioenergetics have demonstrated that electron transport chain enzyme activity (such as rotenone-sensitive NADH:O2 oxidoreductase activity) in individuals with type 2 diabetes is reduced by approximately 40% to 50% compared to lean healthy controls (e.g., 0.56 vs. 0.95 units/mU creatine kinase in Kelley et al., 2002; subsarcolemmal mitochondrial activity reduced substantially in Ritov et al., 2005). However, this reduction reflects specific ex vivo electron transport chain assays in small observational biopsy cohorts rather than an overall 50% loss of total in vivo whole-body mitochondrial function across all tissues or all diabetic individuals, where differences often reflect lower mitochondrial volume density/content, physical inactivity, and obesity rather than an intrinsic 50% global deficit.
- supports: Dysfunction of mitochondria in human skeletal muscle in type 2 diabetes. (Diabetes 2002) · cited 2333x in the literature
"NADH:O(2) oxidoreductase activity was lowest in type 2 diabetic subjects and highest in the lean volunteers (lean 0.95 +/- 0.17, obese 0.76 +/- 0.30, type 2 diabetes 0.56 +/- 0.14 units/mU creatine kinase; P < 0.005)." (abstract, results, passage verified)
pubmedfull study (doi) - partial: Deficiency of subsarcolemmal mitochondria in obesity and type 2 diabetes. (Diabetes 2005) · cited 891x in the literature
"Overall electron transport chain activity was similar in type 2 diabetic and obese subjects, but subsarcolemmal mitochondria electron transport chain activity was reduced in type 2 diabetic subjects (0.017 +/- 0.003 vs. 0.034 +/- 0.007 units/mU creatine kinase [CK], P = 0.01) and sevenfold reduced compared with lean subjects (P < 0.01)." (abstract, results, passage verified)
pubmedfull study (doi) - context: Deficiency of electron transport chain in human skeletal muscle mitochondria in type 2 dia… (American journal of physiology. Endocrinology and metabolism 2010) · cited 285x in the literature
"The specific activity of NADH oxidase (per mg cardiolipin) and NADH oxidase/citrate synthase and NADH oxidase/beta-HAD ratios are reduced two- to threefold in both T2DM and obesity." (abstract, results, passage verified)
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Human muscle performance peaks around the third decade of life, after which people lose approximately 10% of muscle strength and mass every 10 years, with loss accelerating beyond 10% per decade in their 60s.
"So when we are in our 30s, we peak in our muscle performance around the third decade of life, and following that, every 10 years we're losing 10% of muscle strength and muscle mass, okay? And that accelerates even bigger than 10% in our 60s." (said at 0:31:43)
The speaker's general trajectory is broadly accurate but conflates the rates of loss between muscle mass and muscle strength/power. Muscle mass and performance typically peak around the third decade of life. However, skeletal muscle mass declines at a slower rate after age 30 (typically estimated at 3% to 8% per decade, or roughly ~15% total between the third and eighth decades in sedentary adults), whereas muscle strength and power decline at higher rates of approximately 10% to 15% per decade. Longitudinal studies confirm that strength loss accelerates further in older age (past age 60–70).
- context: Longitudinal muscle strength changes in older adults: influence of muscle mass, physical a… (The journals of gerontology. Series A, Biological sciences and medical sciences 2001) · cited 928x in the literature
"The rates of decline in isokinetic strength averaged 14% per decade for knee extensors and 16% per decade for knee flexors in men and women. Women demonstrated slower rates of decline in elbow extensors and flexors (2% per decade) than men (12% per decade). Older subjects demonstrated a greater rate of decline in strength." (abstract, results, passage verified)
pubmedfull study (doi) - context: Quadriceps maximal power and optimal shortening velocity in 335 men aged 23-88 years. (European journal of applied physiology 2005) · cited 92x in the literature
"The decline in P(max) across the adult life span (10.7% per decade) was greater than the usually reported decrease in maximal muscle strength. Power decreased already after the fourth decade. Both muscle mass (4.1% decline for LTVest or 3.4% for quadriceps mass per decade) and upsilon(opt) (6.6% decline per decade) contributed to the decrease in power." (abstract, results, passage verified)
pubmedfull study (doi) - context: What is sarcopenia? (The journals of gerontology. Series A, Biological sciences and medical sciences 1995) · cited 604x in the literature
"In sedentary individuals, the main determinant of energy expenditure is fat-free mass, which declines by about 15% between the third and eighth decade of life, contributing to a lower basal metabolic rate in the elderly." (abstract, results, passage verified)
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