Sports Med DOI 10.1007/s40279-014-0235-1
LETTER TO THE EDITOR
Reference Selection Influences the Reliability of Conclusions Fre´de´ric Noe´ • Jacques Cre´mieux • Nicolas Vuillerme Philippe Perrin • Ge´rome C. Gauchard
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Ó Springer International Publishing Switzerland 2014
We read with great interest the article by Zemkova [1] titled ‘‘Sport-specific balance’’ recently published in Sports Medicine. The main objective of this article was to investigate the effects of different forms of exercise on balance maintenance and to gain insight into the associated physiological mechanisms while also examining how these effects were modulated by sporting expertise. Whereas two recently published reviews [2, 3] focused on the long-term effects of sports exercise while analyzing the relationship between sports expertise and postural control, the originality of Zemkova’s work was to deal with the short-term F. Noe´ (&) Laboratoire Activite´ Physique, Performance et Sante´ (EA 4445), De´partement STAPS, Universite´ de Pau et des Pays de l’Adour, ZA Bastillac Sud, 11 rue Morane Saulnier, 65000 Tarbes, France e-mail:
[email protected] J. Cre´mieux Laboratoire de Motricite´ Humaine E´ducation, Sport, Sante´, Universite´ de Toulon, UFR STAPS Baˆt. K-Campus La Garde, 83957 La Garde, France N. Vuillerme Laboratoire AGIM, Faculte´ de Me´decine, Baˆt. Jean Roget, 38706 La Tronche, France N. Vuillerme Institut Universitaire de France, Paris, France P. Perrin G. C. Gauchard EA 3450 DevAH-De´veloppement, Adaptation et Handicap, Re´gulations cardio-respiratoires et de la motricite´ Universite´ de Lorraine, UFR STAPS de Nancy, 30, rue du Jardin Botanique, 54600 Villers-le`s-Nancy, France P. Perrin Laboratoire d’Analyse de la Posture, de l’Equilibration et de la Motricite´, Hoˆpitaux de Brabois, CHU de Nancy, 54500 Vandoeuvre-le`s-Nancy, France
effects of sports exercise while considering the specificities induced by the performance of different types of exercises. This study also differed from another recent review article about the short-term effects of exercise, which focused on the impact of fatigue [4]. In Zemkova’s work [1], attention was paid to the assessment of balance in sport-specific conditions with the aim of designing specifically oriented, balance-training programs and optimizing the evaluation of the effect of these programs. The author presented a substantial number of experimental studies that analyzed postural sway during and after a wide range of laboratory and/or sport-specific standing conditions. Hence, Zemkova emphasized the importance of adjusting laboratory testing while using exercises that match sport-specific performance as closely as possible to determine accurately their specific effect on balance. Nevertheless, the author’s approach to this interesting topic raises some questions that we discuss below. In a previous issue of Sports Medicine, Zemkova and Hamar published an article titled ‘‘Physiological Mechanisms of Post-Exercise Balance Impairment’’ [5]. Even though this article was mainly concerned with the different physiological mechanisms of post-exercise balance impairment, some redundancies could be found with Zemkova’s subsequent review article in Sports Medicine [1], particularly in considering the second part of the paper, which analyzed the evolution of postural sway after several types of sports exercise. Indeed, among the 76 references used in the first review [5], virtually half of them were included in the subsequent review article [1] (37 common references). All the studies considered by the author that were specifically in line with the topic of this article included experienced sportspeople (mountaineers, skiers, weightlifters, dancers, synchronized swimmers, gymnasts, icehockey players, professional rifle shooters, basketball
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players, judoists, cyclists, soccer players), whose balance abilities were sometimes compared with those of control subjects. Hence, the long-term effects of sport expertise were clearly addressed in this article. Nevertheless, these effects of expertise were only partially discussed and many relevant references relative to this aspect were lacking. Inclusion of these references and a more in-depth discussion of sporting expertise would have refined the conclusions drawn by the author, as judiciously underlined by Professor Thierry Paillard in a previous letter to the editor [6]. Zemkova considered exclusively the mean center of pressure (COP) velocity as ‘‘a reliable measure of postural stability’’ to investigate ‘‘the effects various types of exercise have on balance performance’’. Nevertheless, there is no obvious relationship between balance performance and postural stability [7], and COP velocity is not necessarily the most reliable COP parameter that can be used to analyze balance performance and/or postural stability [8]. For example, in paragraph 3.3, the author drew the conclusion that postural stability in mountaineers was not affected by the height of the support whereas control subjects exhibited increased postural sway velocity when standing above the ground. However, many studies on the effects of exposure to heights (e.g., Brown et al. [9]) have shown that basic COP time-series data such as velocity were not as sensitive as frequency or diffusion parameters for instance. In this example, the author should have been more moderate in her conclusions based on COP velocity data (and when referring to only one of her own studies). Indeed, in a recent study, Wade et al. [10] did not describe concordant results while reporting a degradation of postural control with expert subjects exposed to elevated surfaces. Although the method used for the literature search was rather restrictive to fit the specificity of the addressed topic, with an emphasis ‘‘put on studies in which the relationship between parameters of balance and sport performance was proved’’ [1], the absence of clear selection criteria can be questioned. Indeed, the following exclusion criterion highlighted by the author was somewhat ambiguous: ‘‘additionally, most of the studies were excluded because they did not meet the minimum requirements of an experimental study design’’. The author should have provided more details about what these ‘‘minimum requirements’’ implied insofar as numerous studies that could have contributed relevant information on this topic have not been included in the review. When applying the criteria presented in the Methods section, one can find a number of studies published in internationally indexed reviews that fit these criteria and that have not been included in this
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review. Indeed, 104 references were considered by the author in this review article. When analyzing these references, virtually two thirds of them (66 references) were the author’s own research (38 references of other authors). Among the author’s own 66 references, 32 were conference proceedings, 2 were book chapters, and 32 were articles mainly written in the Slovakian language (this classification might suffer from some errors because it was difficult to differentiate between articles or conference proceedings, the titles and details of which were in the Slovakian language). We also did not manage to obtain most of these references while searching the MEDLINE database, although the author first cited MEDLINE when itemizing the electronic databases that were used for the literature search [1]. Furthermore, the reasoning underlying Zemkova’s article is built entirely on her own references and neglects many studies that are relevant to the topic of sportspecific balance. All the 38 references from other authors are used to provide general insights about physiological mechanisms of balance control. This sort of selectivity in the choice of the references can engender questions among readers who can logically consider that some of the conclusions of this article have to be considered with caution. Acknowledgments The authors have no potential conflicts of interest that are directly relevant to the content of this letter.
References 1. Zemkova´ E. Sports-specific balance. Sports Med. 2014;44(5):579–90. 2. Hrysomallis C. Balance ability and athletic performance. Sports Med. 2011;41:221–32. 3. Kiers H, van Dieen J, Dekkers H, et al. A systematic review of the relationship between physical activities in sports or daily life and postural sway in upright stance. Sports Med. 2013;43:1171–89. 4. Paillard T. Effects of general and local fatigue on postural control: a review. Neurosci Biobehav Rev. 2012;36(1):162–76. 5. Zemkova E, Hamar D. Physiological mechanisms of post-exercise balance impairment. Sports Med. 2014;44(4):437–48. 6. Paillard T. Sport-specific balance develops specific postural skills. Sports Med. 2014. [Epub ahead of print]. 7. Van Emmerik RE, van Wegen EE. On the functional aspects of variability in postural control. Exerc Sport Sci Rev. 2002;30(4):177–83. 8. Murray MP, Seireg AA, Sepic SB. Normal postural stability and steadiness: quantitative assessment. J Bone Joint Surg Am. 1975;57(4):510–6. 9. Brown LA, Polych MA, Doan JB. The effect of anxiety on the regulation of upright standing among younger and older adults. Gait Posture. 2006;24(4):397–405. 10. Wade C, Davis J, Weimar WH. Balance and exposure to an elevated sloped surface. Gait Posture. 2014;39(1):599–605.
