Human movement science

An early afternoon in late March, I am of looking out over the spring-like Karolinska Institutet campus in Stockholm and thinking about some of the discoveries originating from the neighbouring buildings. The house closest to my window was once the prestigious Anatomy–Histology department. Today, this department does not exist, but the Petrén Lecture hall remains to commemorate the legendary anatomist Ture Petrén. I still have a vivid memory of Ture Petrén as a rather strict lecturer and examiner during my anatomy course in the fall of 1966. Petrén’s close collaborator in the Anatomy department Sven Carlsöö worked on the biomechanics of the musculoskeletal system and wrote his thesis in 1952 on the ‘Nervous coordination and mechanical function of the mandibular elevators’ at the Royal Gymnastic Central Institute (GCI) in Stockholm. This Institute had been founded in 1813 by Pehr Henrik Ling, the father of medical gymnastics. Carlsöö was a pioneer in the area of human movement sciences and was active at a time where this research field underwent strong development owing to the entrance of computers. Carlsöö’s book ‘How man moves’ (Carlsöö 1972) is a classical publication in this area and furthermore contains analyses of different sport-specific movements. In his January 2012 Editorial, the Acta Physiologica Chief Editor wrote about another person, who made an important contribution to human movement science, Emil Du Bois-Reymond (Persson 2012). Du Bois-Reymond, the father of experimental electrophysiology, made observations and performed method developments that paved the way for Electromyography. Interestingly, Du Bois-Reymond once had his laboratory in the same building at the Charité in Berlin, where the Acta Physiologica Chief Editor Pontus Persson and Editorial secretary Carola Neubert now reside. Today, research on human movement science, or kinesiology, integrates knowledge from many different scientific areas such as neurophysiology, neurology, muscle physiology and biomechanics, with an overall aim to obtain increased insight into human motor behaviour. By tradition, this is a main area in Acta Physiologica. Although the importance of the motor cortex has been recognized for almost one and a half centuries (Fritsch & Hitzig 1870), it has become clear that there are different levels of motor cortical involvement in specific tasks. The homunculus is the well-known motor map with the body’s musculature draped over the motor cortex that implies that each small area in the motor cortex corresponds to a particular movement (Penfield & Rasmussen 1952). The homunculus was based on results from motor evoked potential research that involved direct observations by stimulating the human brain with weak electrical shocks in conscious patients who were undergoing surgery (Penfield & Boldrey 1937). Although much of these early data are still valid, it is now known that even for the precise movements of the hand, the cortical input arises from a much wider region of the cortex. In addition, cortical areas interact in different ways with each other and with spinal interneurones and motor neurones to produce specific movements. This is discussed in a recent review in Acta Physiologica (Petersen et al. 2010), which also describes several sources of nonlinearity between the cortical and the motoneuronal output. Such sources may include varying efficacy of the corticomotoneuronal synapse (Hultborn et al. 1996), but also the actual motoneuronal firing rate, which determines the responsiveness of the motor neurone pool (Matthews 1999). The motoneuronal output may also be changed with ageing and it was recently shown that the maximal neural drive to elbow flexors and extensors is impaired in older adults. This occurs most notably in the elbow flexors with negative consequences for upper limb motor control (Dalton et al. 2010). The decreased ability of the muscle fibres to produce force with fatigue is accompanied by a fatigueinduced decline in the firing rate of motor neurones. This is partly caused by a reduction in the discharge rate of stimulatory 1a afferent fibres from muscle spindles (Vallbo 1974, Macefield et al. 1991), but also by increased activity in inhibitory groups III and IV small diameter muscle afferents (sensitive to mechanical, thermal and chemical stimuli) (Martin et al. 2006). The latter may be dependent on muscle type and mainly seems to exist in extensor muscles. Changes in motoneuronal firing may give rise to compensatory adaptations in the cortical drive to motor neurones, including a changed excitability of inhibitory circuits controlling corticospinal output (Seifert & Petersen 2010). In a recent Acta Physiologica article, evidence was presented that Writer’s cramp, a focal dystonia of the hand owing to repetitive, stereotyped writing movements, most likely involves an