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Question 1

Integumentary (research level: medium)

Answer

Yoga: Bikram, hot yoga (general).

During Bikram and other heated forms of yoga, the skin functions as the primary thermoregulatory interface. Sessions occur at 30–52°C, producing increased core temperature, vasodilation, sweating, plasma volume changes, and upregulation of heat shock protein 70 (HSP70). With non-heated yoga styles, these changes are not significant.

Please note that the cardiovascular load of hot yoga isn’t appropriate for all populations.

References: Willmott et al. (2025), Bourbeau et al. (2021).

Question 2

Skeletal (research level: medium)

Answer

Yoga: hot yoga, Iyengar, hatha.

Chronic hot yoga practice has been associated with increased bone mineral density as part of a broader set of cardiometabolic and functional adaptations. Older-adult research on yoga and balance, especially on Iyengar and hatha, also indirectly supports skeletal health through reduced fall risk, though direct measurement of bone outcomes in non-heated styles is sparse.

References: Willmott et al. (2025), Ko et al. (2023).

Question 3

Muscular (research level: high)

Answer

Yoga: Iyengar, hatha, hot yoga.

Older-adult yoga research is dominated by Iyengar and hatha styles, with measurable improvements in balance, flexibility, and muscle strength. Hot yoga practice produces similar improvements alongside its thermoregulatory adaptations. Effect sizes in meta-analysis: balance SMD* = 0.81, muscle strength SMD = 0.49, flexibility SMD = 0.38. Note that these effects come from the populations (older adults) and styles studied — they are not necessarily superior to what other yoga styles would produce if studied.

References: Ko et al. (2023), Sivaramakrishnan et al. (2019), Willmott et al. (2025).

* SMD stands for Standardized Mean Difference. It’s a number indicating the effect of something between two groups, e.g., yoga vs another activity. A number between 0.2 - 0.5 indicates a small effect, 0.5 - 0.8 a medium effect, and over 0.8 a large effect.

Question 4

Nervous (research level: high)

Answer

Yoga: Bikram, hatha, integrated yoga, Iyengar, Kundalini, restorative, Sahaja yoga meditation, Sudarshan Kriya yoga.

In yoga, the nervous system is most extensively studied.

The autonomic nervous system (HRV, vagal tone) has been monitored during hatha, Iyengar, Sudarshan Kriya, integrated yoga, restorative, and Bikram practice. Results indicate increased HRV and vagal dominance during practice, and elevated resting vagal tone in regular practitioners compared to non-practitioners.

In regard to autonomic changes, restorative yoga shows a strong and consistent effect. A restorative yoga intervention substantially increased cardiac vagal tone and reduced heart rate compared to two control conditions.

For central nervous system structure and function, neuroimaging studies — using long-term hatha (most common), Sahaja yoga meditation, Kundalini, integrated yoga, and unspecified practitioners — have found greater gray matter volume in the insula and hippocampus, increased prefrontal cortical activation, and connectivity changes in the default mode network. Findings vary across styles. Please note that active control groups, such as other forms of physical activity, are rarely used, increasing the risk of bias and making it hard to attribute effects solely to yoga.

References: van Aalst et al. (2020), Tyagi et al. (2016), Khattab et al. (2007), Gothe et al. (2019).

Question 5

Endocrine (research level: high)

Answer

Yoga: hatha, integrated yoga, Sudarshan Kriya, Bikram, restorative.

Two endocrine pathways have been measured: the HPA axis* (cortisol) and glucose-insulin regulation.

For cortisol, a 2025 network meta-analysis of 44 randomized controlled trials (a type of experimental study) found that yoga produced the largest cortisol-reduction effect among exercise modalities in populations with psychological distress (SMD = -0.59). Bikram practice specifically reduced cortisol reactivity to stress over 8 weeks. Restorative yoga produced measurable changes in diurnal cortisol dynamics in patients with metabolic syndrome. Please note that the used references indicate a high risk of bias, i.e., small samples, weak controls, and inadequate blinding.

For glucose and insulin, yoga interventions in type 2 diabetes have produced significant reductions in fasting glucose (−31.98 mg/dL), HbA1c (−0.73%), fasting insulin, and HOMA-IR. Notably, both vigorous and restorative styles show glycemic effects, suggesting the mechanism is not purely metabolic load but likely also involves the autonomic (nervous) and HPA pathways.

References: Li et al. (2025), Akhtar et al. (2023), Kanaya et al. (2014), Corey et al. (2014), Willmott et al. (2025).

* HPA axis stands for hypothalamic-pituitary-adrenal axis, a nervous and endocrine system overlap, i.e., neuroendocrine, that regulates stress.

Question 6

Cardiovascular (research level: high)

Answer

Yoga: hatha, Iyengar, integrated yoga, Bikram, hot yoga (general), restorative.

This is the system where style matters most for the acute response.

During a 90-minute Bikram session, the mean heart rate reached 126.6 bpm with a maximum of 168.1 bpm; systolic blood pressure did not increase, but diastolic blood pressure decreased significantly. Chronic hot yoga produces cardiometabolic adaptations, including changes in body composition, lipid profiles, and macrovascular function.

Restorative yoga produces the opposite acute pattern — reductions in heart rate and blood pressure, with increased cardiac vagal tone.

Across all studied styles, yoga reduces resting blood pressure (particularly systolic) and waist circumference in populations with metabolic syndrome. So vigorous and hot styles provide a training stimulus for the cardiovascular system; passive styles provide a recovery stimulus.

References: Hurtado et al. (2019), Willmott et al. (2025), Cramer et al. (2016).

Question 7

Lymphatic / Immune (research level: medium)

Answer

Yoga: hatha, integrated yoga, Sudarshan Kriya, pranayama-meditation combinations.

Lymphatic engagement specifically (lymph flow, drainage) is frequently claimed in yoga teaching but rarely measured directly. The bulk of measurement in this category is on immune function and inflammation.

Across 26 randomized controlled trials, 24 reported favorable inflammatory marker outcomes regardless of yoga type, condition, or duration. Most-studied markers: IL-6, TNF-α, and CRP, with consistent reductions. Gene expression studies show yoga downregulates pro-inflammatory genes (IL-6, TNF-α, NF-κB) and upregulates anti-inflammatory genes (TGF-β, FoxP3, IL-10), and influences DNA repair (OGG1), mitochondrial regulation (AMPK, SIRT-1), and epigenetic markers.

References: Mishra et al. (2024), Giridharan et al. (2025), Falkenberg et al. (2018).

Question 8

Respiratory (research level: high)

Answer

Yoga: pranayama-focused interventions, integrated yoga, hatha.

The strongest respiratory effects in the yoga literature come from pranayama-heavy interventions specifically — the breath-training component, not asana practice. What appears in reviews as "yoga's respiratory effects" is often really "breath training within yoga."

Across 10 randomized controlled trials (1007 patients), yoga interventions significantly improved FVC% (+3.03 L), FEV1 (+0.47 L), and FEV1% in clinical populations. In asthma specifically, a meta-analysis of 15 trials found yoga improved FEV1 (SMD* = 0.96), FVC, peak expiratory flow rate, and quality of life. Effects are also documented in COPD. Improvements include lung volumes and respiratory muscle strength (MIP, MEP).

References: Rathore et al. (2025), Anshu et al. (2023), Liu et al. (2014).

* SMD stands for Standardized Mean Difference. It’s a number indicating the effect of something between two groups, e.g., yoga vs another activity. A number between 0.2 - 0.5 indicates a small effect, 0.5 - 0.8 a medium effect, and over 0.8 a large effect.

Question 9

Digestive (research level: high)

Answer

Yoga: integrated yoga, Iyengar, hatha.

Yoga interventions improve symptom severity, mood-related symptoms, and quality of life in irritable bowel syndrome (IBS). A 2025 systematic review on IBS specifically found moderate-to-large effects on symptom severity (Cohen's d range 0.37–3.60). Effects are also documented in inflammatory bowel disease and gastrointestinal cancer populations. The proposed mechanism involves vagal tone modulation via the gut-brain axis.

Please note that the research quality varies, and yoga style is rarely disaggregated (i.e., categorized) in this literature.

References: Aktaş et al. (2024), Pavan et al. (2025), D'Silva et al. (2020).

Question 10

Urinary (research level: low)

Answer

Yoga: hatha, integrated yoga.

Direct yoga research on urinary system function is thin. Some emerging evidence on pelvic floor engagement in incontinence populations exists, but is methodologically weak and rarely disaggregated by style. This is a system where claims outpace measurement.

References: Huang et al. (2014).

Question 11

Reproductive (research level: low)

Answer

Yoga: hatha, integrated yoga.

Research is mostly symptom-focused rather than mechanism-focused. Studied populations include menopausal symptoms, polycystic ovary syndrome (PCOS), menstrual disorders, and infertility-related stress. Effects appear to operate primarily through the HPA axis and autonomic pathways rather than through direct engagement of the reproductive organs.

Please note that the research is limited and primarily symptom-focused rather than mechanistic.

References: Cramer et al. (2018), Thakur et al. (2021).

Yoga and Anatomy by Planes: How Holistic is Yoga

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Published on

Yoga and the organ systems

Integumentary (research level: medium)

Skeletal (research level: medium)

Muscular (research level: high)

Nervous (research level: high)

Endocrine (research level: high)

Cardiovascular (research level: high)

Lymphatic / Immune (research level: medium)

Respiratory (research level: high)

Digestive (research level: high)

Urinary (research level: low)

Reproductive (research level: low)

Sporadic Newsletter

Willem Kramer

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