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Leonardo Da Vinci (1452-1519) already recognised that muscles are fibrous tissue to which nerves are connected that initiate contraction. Andreas Vesalius (1514-1564) utilized human dissection to provide the first truly detailed anatomical record of the human musculature in De Humani Corporis Fabrica (1543). However, the physiological mechanism of contraction remained elusive. The 17th century introduced iatrophysics (or iatromechanics), a school of thought that sought to explain all physiological laws in terms of mechanical forces and mathematical formulas. The primary figure in this movement was Giovanni Alfonso Borelli (1608-1679), often called the father of biomechanics. Borelli and Marcello Malpighi (1628-1694) were both founder-members of the short-lived Academia del Cimenti, an Italian scientific academy founded in 1657. In his work De Motu Animalium (1680), Borelli applied Galilean mechanics to the human frame, treating bones as levers and muscles as the sources of power. Borelli made several groundbreaking observations regarding the musculoskeletal system. He recognized that muscles generally attach close to the joints (the pivots), resulting in a mechanical advantage of less than unity. This meant muscles had to produce forces far greater than the loads they moved to amplify displacement and velocity. Borelli hypothesized that contraction was generated by a “succus nerveus” (nerve juice) interacting with substances in the muscle to cause a fermentation process.
A competing theory was the balloonist theory proposed by Thomas Willis (1621-1675), which stated that muscle contraction was caused by the inflation of muscle by animal spirits, fluid or by a reaction of animal spirits with blood components. These would reach the muscle through nerves that were hollow and the movement of spirits through them propelled muscle motion. Niels Stensen (1638-1682) was the first to propose that muscle contraction involved a geometrical reorganization of the muscle fibers. The balloonist theory was put to rest by Jan Swammerdam (1637-1680) and Francis Glisson (1597-1677). Swammerdam demonstrated that muscles did not change in volume when they contract by placing a frog muscle in an airtight syringe with a drop of water at the tip; when stimulated, the water level did not rise, proving that no fluid or air had entered the muscle. Glisson corroborated this with an experiment involving a man flexing his arm under water, noting no change in the displacement of the liquid.
Around the same time Leeuwenhook noted the striation of muscle tissue and based on these observations William Croone (1633-1684) suggested in 1675 that these might be the units of contraction.
In 1752, Albrecht von Haller (1708-1777) demonstrated experimentally that irritability (contractility) was an intrinsic property of all muscular tissue; and distinguished between the sensibility of nerve impulses and the irritability of muscular contraction.
The late 18th century witnessed a paradigm shift from mechanical models to electricity. Luigi Galvani’s experiments (1792) on frog nerves and muscles demonstrated that bioelectricity could trigger contraction. This “animal electricity” provided the first evidence that the nervous signal was an inherent force within living tissue. Alessandro Volta’s subsequent invention of the voltaic pile allowed for more systematic experimentation, ultimately leading to the field of electrophysiology (see the “The concept of the membrane potential and the action potential”). However, Volta never accepted the concept of endogenous animal electricity as proposed by Galvani. Not much progress was made until the end of the 18th beginning of the 19th century when Gustav Retzius (1842-1919) and Emilio Veratti (1872-1967) described the anatomical structure of sarcomeres in much more detail.
These structural insights remained almost forgotten for 60 years. H. Stanley Bennett wrote in 1960: “It is astonishing that a structure once described as accurately and as beautifully as the reticulum was by Veratti (1902) should have so quickly become almost lost to man’s knowledge”. In the 1960’s the fine structure of muscle cells was worked out in detail by electron microscopy by several groups (H.S. Bennet, F.O. Simpson and S.J. Oertelis, D.A. Nelson and E.S. Benson, C. Franzini-Armstrong, C. and K.R. Porter, S. Page)
As the 19th century progressed, the study of muscle became increasingly professionalized. Eduard Weber (1806–1871) made foundational contributions to early muscle physiology by studying the mechanics of muscle contraction, the spinal cord’s role in reflexes, and the neural control of movement. His work—often conducted alongside his brother Ernst—helped shift physiology from descriptive anatomy to quantitative, experimental science. In Britain, William Sharpey (1802–1880), appointed Professor at University College London in 1836, became the “Father of British physiology” by emphasizing experimental training. The founding of The Physiological Society in 1876 and of the Journal of Physiology in 1878 provided the institutional framework for muscle research. These years were also marked by legal and ethical debates, such as the 1875 Royal Commission on animal experimentation and the “Brown Dog affair” (1903–1910), reflecting the societal tension surrounding the rise of physiological research involving animal experiments.
Johannes Peter Müller also had a strong influence on muscle physiology through his school of thought. Hermann von Helmholtz (1821-1883) investigated in 1848 the transformation of energy in muscle tissue. used a thermopile and galvanometer to measure the minute temperature changes in contracting muscle, proving that muscles produce heat as a byproduct of activity and supporting the principle of energy conservation. Eduard Pflüger (1829-1910) was a student of Du Bois-Reymond (see “The concept of membranes, the membrane potential, and the action potential”). He expanded on the work of his mentor, du Bois-Reymond, to create a set of rules for how muscles respond to electricity. He determined that the contraction of a muscle depends on the direction, strength, and polarity (anode vs. cathode) of the electrical current (Pflügers Law of contraction). This became a fundamental principle for medical diagnostics and the use of galvanic currents in therapy for decades.
Adolf Fick (1829-1901) introduced the concepts of isotonic (constant tension) and isometric (constant length) muscle contractions, which are still the primary ways we categorize exercise and physical therapy today. He studied skeletal and heart muscle, and calculated expenditure of energy and development of heat during muscle contraction. This was done using delicate instruments which retained their practical value for almost a century. He concluded that chemical energy is directly transferred to mechanical energy.
Wilhelm Kühne (1837-1900) worked at the intersection of chemistry, microscopy, and classical muscle physiology. He introduced the term myosin in its modern biochemical sense. He isolated a coagulable muscle protein from skeletal muscle and showed that this protein was responsible for the gel–sol transitions occurring in muscle extracts. He demonstrated that the protein could form a clot-like material when extracted—hence his early name fibrinoplastin. He later renamed it myosin, establishing the biochemical identity of the contractile machinery.
Kühne was one of the earliest physiologists to argue that muscle contraction involves enzymatic catalysis. He proposed that muscle contains “ferments” (early term for enzymes) that break down chemical substrates, release energy, and thereby power contraction.
Working in the tradition of Helmholtz, Kühne performed careful measurements of heat production during contraction and showed that muscle energetics must involve internal chemical changes. This reinforced the idea that contraction is not a purely mechanical phenomenon but a chemical transformation.
Kühne was a gifted microscopist. He described the sarcomeric banding pattern with unusual clarity, and linked structural changes to physiological states (rest, rigor, contraction), thus establishing the structural basis for later models of contraction.
He performed classic experiments on rigor mortis, showing that rigor is a chemical process, not simply mechanical stiffening, involving coagulation of muscle proteins (myosin).
Max von Frey (1852-1932) was the first to notice that the majority of oxygen was consumed by muscle not during exercise but during the recovery phase. He linked this to the production of lactate thereby forming the basis of muscle biochemistry that was only understood in the 20th century.
In the 20th century researchers started using newly developed intervention tools such as electrodes that could be inserted into ganglia or neuromuscular junctions and measurement devices such as the string galvanometer and the cathode ray oscilloscope. Using such instruments, Keith Lucas (1879-1916) established in 1909 that when stimulated, muscle fibers respond in an “all-or-none” manner.
Between 1910 and 1920, August Krogh (1874-1949) in Denmark developed instruments such as the tilting spirometer, the electromagnetic bicycle ergometer, and an apparatus for gas analysis. These instruments allowed Krogh to demonstrate the relative value of carbohydrate and fat as sources of energy for muscular contraction. Moreover, he showed that an oxygen deficiency developed at the beginning of work, which was not replaced until the conclusion of work. Krogh went on to win the Nobel Prize in Medicine and Physiology in 1920 for his ‘discovery of the regulation of the motor mechanism of capillaries’. He found that the average diameter of open microvessels was wider in working than in resting muscles.
The early 20th century was defined by the rigorous quantification of muscle metabolism and thermodynamics. Frederick Gowland Hopkins (1861-1947) and Walter Morley Fletcher (1873-1933) in 1907 found the connection between lactic acid production and muscle contraction, which spawned the whole field of muscle bioenergetics. Archibald Vivian (A.V.) Hill (1886-1977) and Otto Meyerhof (1884-1951) were awarded the 1922 Nobel Prize for their work in this field. Hill focused on the physical aspects of contraction, using high-precision thermopiles to measure heat production, while Meyerhof explored the biochemical relationship between oxygen consumption and lactic acid production.
Hill’s contributions were foundational for modern exercise physiology. He introduced the concept of maximal oxygen uptake and the idea that the circulatory and respiratory systems impose limits on exercise. Together with Wallace Fenn (1893-1971), he also identified the ‘Fenn effect’, which overturned the older elastic model of muscle. The elastic model had posited that muscle energy expenditure was determined solely by the muscle’s initial length, acting like a stretched spring. Hill and Wallace Fenn demonstrated that muscle energy liberation increases when the muscle performs work, suggesting a more complex active engine.
The mathematical description of muscle force and velocity became a hallmark of this era. The Hill equation provided a quantitative framework for understanding how the rate of energy liberation scales with the load placed on the muscle. This period also saw the discovery of Adenosine Triphosphate (ATP) by Karl Lohmann (1898-1978) in Meyerhof’s laboratory as the energy currency of the cell. Vladimir Engelhardt (1894-1984) and Militsa Lyubimova (1899-1975) discovered in 1939 that myosin acts as an ATPase, directly hydrolyzing ATP to power contraction.
As outlined above, Willy Kühne had already extracted myosin from muscle tissue in 1864. The structural analysis of muscle tissue had to wait until the mid-20th century when muscle research transformed from a study of thermodynamics into a study of molecular structure. Albert Szent-Györgyi (1893-1986) and the Szeged school discovered that the ‘myosin’ described by Kühne was actually two distinct proteins: actin and myosin. They also discovered that myosin would become gel-like over time, a process, which could be reversed by ATP. In 1942, Bruno Ferenc Straub (1914-1996) purified actin and identified its globular (G-actin) and fibrous (F-actin) forms. When combined into actomyosin threads, these proteins contracted in the presence of ATP, marking the first time a biological process was reproduced in vitro using purified components.
Despite these biochemical advances, the physical mechanism of shortening remained a mystery. It was widely believed that the protein filaments themselves contracted or folded. This view was overturned in 1954 by two independent teams—Andrew Huxley (1917-2012, also known for the Hodgkin-Huxley model of the action potential) and Rolf Niedergerke (1921-2011), and Hugh Huxley (1924-2013) and Jean Hanson (1919-1973)—who published back-to-back papers in Nature proposing the Sliding Filament Theory.
Using interference microscopy and electron microscopy, these researchers observed that, first the length of the A-band (myosin filaments) remains constant during contraction and stretch. Secondly, the change in sarcomere length is accounted for by the change in the I-band (actin filaments). Third, shortening occurs because the filaments slide past one another, increasing the degree of overlap.
Hugh Huxley further utilized X-ray diffraction to demonstrate that muscle consists of a hexagonal lattice of filaments where each thick filament is surrounded by a ring of thin filaments. This structural resolution paved the way for the “swinging cross-bridge” model, where the myosin heads bind to actin and undergo a power stroke to pull the filaments toward the M-line.
This work was followed by a more detailed investigation of the structure and function of the contractile unit. Clara Franzini‑Armstrong (born 1938) defined the ultrastructural basis of excitation–contraction (E–C) coupling, especially the architecture of T‑tubules and their relationship to the sarcoplasmic reticulum. This clarified how the surface action potential penetrates deep into the fiber, enabling synchronous activation of the contractile machinery. Her early EM work mapped the triad — the junction of one T‑tubule with two terminal cisternae of the sarcoplasmic reticulum (SR). This helped to establish that E–C coupling is fundamentally an architectural problem.
The identification of the sliding mechanism required a corresponding theory for how contraction is regulated. Sydney Ringer (1835-1910) discovered in 1883 that an isolated frog heart would only continue beating if calcium was present in the bathing solution. This was the first demonstration that Ca²⁺ is essential for muscle function. He also noted that potassium and sodium ions had to be present at the right ratio to sustain the spontaneous beat of the heart. Percy Stiles (1875-1936) confirmed this function in 1901 using smooth muscle cells.
The dependence on Ca2+ was much more difficult to show for skeletal muscle, which largely relies on intracellular calcium stores rather than extracellular sources.
Else Weise found in 1934 that an ultrafiltrate of rat skeletal muscle dispersed in saline contained no detectable Ca2+, implying sequestration of Ca2+ in some cellular structures.
Lewis Victor Heilbrunn (1892-1959) performed classic experiments in 1947 injecting Ca²⁺ into muscle fibers and observing what he thought was a coagulation of protein. These results were widely overlooked or criticised. Takeo Kamada and Haruo Kinosita, however, based their experiments on Heilbrunns worked and provided early evidence that intracellular Ca²⁺ release was involved in skeletal muscle contraction. This provided the first hint that calcium ions inside the muscle fiber were critical.
In an elegant series of experiments Annemarie Weber used EDTA and EGTA buffer systems to control free Ca2+ concentration and established in 1959 that the ATPase activity and the state of contraction of natural actomyosin and myofibrils are unique functions of free Ca2+ concentration. Later in the 1960’s calcium transients could be visualized using the calcium binding protein aequorin.
Setsuro Ebashi (1922-2006) is the central figure in the modern understanding of Ca²⁺ regulation. In the 1950s he identified the ‘relaxing factor,’ later shown to be the sarcoplasmic reticulum (SR) storage of calcium. In 1961 he proposed the calcium concept of contraction and relaxation and showed that the SR relaxes muscle by binding Ca²⁺. In 1966 he discovered troponin, the Ca²⁺ receptor that regulates actin–myosin interaction. Setsuro Ebashi’s work in the 1960s identified ‘native’ tropomyosin and the troponin complex as the calcium-dependent switch for muscle activity. His steric hindrance model explained that in the absence of calcium, the troponin-tropomyosin complex blocks the myosin-binding sites on actin. Calcium binding to tropomyosin C causes a conformational shift, exposing the sites and allowing contraction to proceed.
The initially puzzling ATP-dependent Ca2+-binding process was identified by Wilhelm Hasselbach (1921-2015) as a powerful Ca2+ transport system which derived its energy from the hydrolysis of ATP through a Ca2+-specific transport-ATPase.
In the middle of the 19th century the clinical characterization of muscle diseases began. Guillaume Duchenne de Boulogne (1806-1875) and Edward Meryon (1809-1880) identified the progressive muscle wasting of Duchenne muscular dystrophy. Duchenne’s use of the first muscle biopsy instrument confirmed that these conditions involved pathological changes within the muscle tissue itself.
The measurement of creatine kinase in the blood provided a biomarker for muscle damage. The advent of the electron microscope led to the emergence of ‘congenital myopathies’ as a distinct field of study, while the identification of abnormal mitochondria opened the field of mitochondrial cytopathies. These developments transformed myology into a ‘molecular era’ where gene defects could be identified as the root of inherited muscle diseases.
The identifying of the first fragments of the Duchenne Muscular Dystrophy gene cDNA in 1986 by Louis Kunkel (born 1949) and colleagues was a definitive moment in muscle research history. Subsequently, Kunkel, along with Anthony Monaco and Michel Koenig, characterized the gene as the largest known genomic locus at the time and predicted its protein product, dystrophin. This discovery nucleated a massive research effort into the myofiber membrane cytoskeleton.
Despite the success of the sliding filament theory, two major mysteries remained: the origin of passive elasticity and the phenomenon of residual force enhancement. The search for a ‘third filament’ led to the independent discovery of connectin by Koscak Maruyama (1976) and titin by Kuan Wang (1979). Titin, a giant elastic protein spanning from the Z-disc to the M-line, was found to be the “elephant in the room”—an extraordinarily large protein (>1 MDa) that had been difficult to observe with standard electrophoresis.
John O. Holloszy (1933–2018) is widely regarded as the father of modern exercise biochemistry, a title earned through more than five decades of pioneering research into how the body adapts to physical training. His work reshaped exercise physiology, metabolism research, and even aging science. In 1965, Holloszy published the first demonstration that endurance exercise training doubles mitochondrial content in skeletal muscle. This single discovery opened the modern field of skeletal muscle plasticity, influencing everything from elite athletic training to metabolic disease research.
Holloszy was the first to show that muscle contractions stimulate glucose uptake without insulin. This finding became foundational for understanding how exercise improves glucose control, why it benefits people with insulin resistance or type 2 diabetes, and how muscle acts as a metabolic organ and lifestyle interventions can rival pharmacology in certain contexts.
The modern era of exercise biology was also shaped by advancements in technology. In the case of human research, the reintroduction of the muscle needle biopsy for exercise research by Jonas Bergström and Eric Hultman (1966) illustrates how a relatively simple technological advancement can have major impact on years of future research.
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