Homeostatic Crosstalk between Skeletal Muscle Kinetics, Cardiovascular System and Autonomic Nervous System in Healthy Early Adulthood Age Males of Different Body Types

Introduction: The human musculoskeletal system is controlled by efficient neural processes which is achieved through intricate mechanisms within the cerebral cortex, spinal cord, and muscle cytoarchitecture. Bernstein's work on kinetic redundancy highlighted neural circuits role in muscle trajectory, supported by EMG data (1). Sheldon’s somatotype theory (2), refined by Heath & Carter, categorizes body types based on embryonic development (3). Despite these efforts, muscle synergies during isotonic and isometric contractions and the relationship with somatotypes remain unexplored. Methods: The healthy male participants (n = 11, aged 18–23 years) recruited for study (IEC: 48/IECGMC/October2024). The data acquisition is done using ADInstruments® from lead II ECG, electromyography (EMG) of forearm, pulse transducer and hand grip dynamometer. The exercise protocols implemented were as follows: a) Isometric contraction protocol: Participants performed sustained contractions at 50% of their Maximum Voluntary Isometric Contraction (MVIC), continuing until grip force dropped by 50%. b) Isotonic contraction protocol: Increment of 1 kg loads were lifted through wrist flexion. c) Fitness assessment: Tecumseh Sub-Maximal Step Test was performed. The somatotype classification was done using anthropometric measurements of various sites using Heath and Carter's method. Results: The EMG analysis showed no significant differences in EMG height, RMS, mean power frequency, or median power frequency between ectomorphs and mesomorphs during isometric exercise. However, during isotonic contractions, EMG RMS was significantly higher in ectomorphs (p = 0.0365). Cardiovascular responses revealed significant differences in heart rate, pulse amplitude, and pulse transit time between the two groups during both exercise types (p < 0.0001). Correlations between heart rate and EMG showed significant positive correlations with EMG height and RMS, and negative correlations with mean and median power frequency. Fitness did not correlate with cardiovascular or EMG parameters. HRV showed no significant differences post-intervention. Conclusion: The study compares skeletal muscle activation and cardiovascular responses between ectomorphs and mesomorphs during isometric and isotonic contractions. While muscle activation is similar during isometric tasks, ectomorphs show greater recruitment during isotonic contractions. Cardiovascular adaptability differs significantly between body types, but autonomic modulation does not reach statistical significance. Despite these differences in EMG and cardiovascular responses, prior fitness levels did not influence performance, suggesting that changes were acute, not due to pre-existing adaptations. HRV analysis confirms that these responses are driven by immediate exercise demands. Ectomorphs exhibit stronger autonomic-motor integration supporting endurance, while mesomorphs show balanced efficiency favoring strength-oriented activities. Acknowledgement: I thank UGSRS 2024, (Grant number: 155/24M286) & Department of Physiology for providing the funding, space to work and support during this study. I am obliged to my teachers and subjects without which this study wouldn’t have existed. References: 1. Bernstein NA. The co-ordination and regulation of movements. Pergamon Press, Oxford, 1967. 2. Sheldon W, Stevens SS, & Tucker WB. The varieties of human physique: An introduction to constitutional psychology. New York: Harper & Brothers, 1940. 3. Heath BH & Carter JE. A modified somatotype method. Am J Phys Anthropol. 1967;27:57-74. Undergraduate Student Research Scholarship (UGSRS 2024, Grant number: 155/24M286) This abstract was presented at the American Physiology Summit 2025 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.