ORIGINAL ARTICLE Changes in arm coordination and stroke parameters on transition through the lactate threshold Pedro Figueiredo • Pedro Morais • Joa˜o Paulo Vilas-Boas • Ricardo J. Fernandes Received: 10 July 2012 / Accepted: 15 February 2013 / Published online: 21 March 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract The purpose of the present study was to understand the energetic, biomechanical and coordinative changes occurring throughout the transition of the lactate threshold. Twelve high-level swimmers (six males and six females) performed a paced intermittent incremental pro- tocol of 7 9 200 m (0.05 m s -1 increments and 30 s intervals). The stroking parameters (stroke rate and stroke length) and the index of coordination (IdC) were assessed by analysis of video recordings from aerial and underwater side-view cameras. Energy cost (C) was determined by the ratio energy expenditure/velocity. Energy expenditure was determined by measuring oxygen uptake _ V O 2 À Á and blood lactate concentrations ([La - ]). The swimming velocity at the inflection point of stroke rate, stroke length, IdC, _ V O 2 , and [La - ] was determined (m s -1 ). The results showed that stroke rate, stroke length, IdC, _ V O 2 , and [La - ] all exhibited inflection point as a function of swimming velocity, and these velocities were highly correlated with the velocity at [La - ] inflex (1.35 ± 0.07 m s -1 ; R = 0.99, P \ 0.001). Furthermore, these values were not significantly different (P [ 0.05), and Bland–Altman plots estimations were almost unbiased. These findings seem to confirm that as swimming velocity increases and lactate threshold is sur- passed, it induces changes in stroke mechanics and orga- nization suggesting an important biomechanical, coordinative and metabolic boundary between moderate and heavy intensity domains. Keywords Motor control Á Biomechanics Á Front crawl Á Swimming Á Metabolic parameters Á Lactate threshold Introduction Previously, the physiological factors influencing human movement coordination have been applied to front crawl swimming (e.g. Sparrow and Newell 1998), and more recently, a direct relationship between front crawl inter-arm coordina- tion and physiological parameters, such as energy cost (C), has been demonstrated (Fernandes et al. 2010a, b; Komar et al. 2011; Seifert et al. 2010). This suggests that coordinative and biomechanical parameters are related to physiological factors, whereby swimmers naturally adopt a movement pattern, in a process termed self-optimization, to achieve their goal of swimming faster while becoming fatigued. An index of coordination (IdC) has been developed by Chollet et al. (2000) offering the opportunity to study the relationship between front crawl swimming coordination and factors such as fatigue. However, although C and energy expenditure ( _ E) have a linear relationship with IdC, changes of both aerobic (oxygen uptake, _ V O 2 ) and anaerobic (blood lac- tate concentrations, [La - ]) pathways with velocity are not linear. At moderate intensities, the assessment of an athlete’s lactate threshold is important in establishing individual Communicated by David C. Poole. P. Figueiredo (&) Á P. Morais Á J. P. Vilas-Boas Á R. J. Fernandes Centre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto, Rua Dr. Pla´cido Costa, 91, 4200-450 Porto, Portugal e-mail: spafg@vofafone.pt P. Figueiredo Higher Education Institute of Maia (ISMAI), Av. Carlos Oliveira Campos, Avioso S. Pedro, 4475-690 Maia, Portugal J. P. Vilas-Boas Á R. J. Fernandes Porto Biomechanics Laboratory, University of Porto, Rua Dr. Pla´cido Costa, 91, 4200-450 Porto, Portugal 123 Eur J Appl Physiol (2013) 113:1957–1964 DOI 10.1007/s00421-013-2617-8