The roller sport or inline skating is a rapidly expanding sport governed by the International Federation of Roller Sports (FIRS, 2016). It is among rare sports that have equal participation of men and women (International Olympic Committee, 2013). Although researchers identified a high risk of injuries related to inline skating (Nguyen and Letts, 2001; Tan et al., 2001), more than 50 million people worldwide practice this sport (International Olympic Committee, 2013). This is not surprising considering that numerous studies showed inline skating to have positive effects on cardiovascular health (Melanson et al., 1996, Orepic et al., 2014) and postural control (Muehlbauer et al., 2013; Taube et al., 2010). Moreover, it has been shown that inline skating helps to maintain specific abilities during off-season in complementary sports (de Boer et al., 1987; Crawford and Holt, 1991; Carroll et al., 1993; Duquette, 2000; Kroll et al., 2003; Stoggl et al., 2008), and in general enhances physical fitness in athletes (Martinez et al., 1993; Wallick et al., 1995). However, in order to become competent in this sport, long-term systematic training is required. In the early stages it is important to adjust to the unusual underfoot media (wheels), while in later stages skating technique becomes the focus (Powell and Svensson, 1998), which differs from the inborn pattern of human movement. Inline skating has thus been regarded as one of the most demanding sports in terms of motor skill requirement (Rinne et al., 2007). Due to frequent accelerations, starts and direction changes, which require rapid eccentric-concentric muscular efforts (Millet et al., 2003; Dellal et al., 2010), it depends predominately (~70%) on anaerobic metabolism (Reilly et al., 1990). However, the extent to which anaerobic processes participate in energy supply in inline skating depends on loading duration as well as on technical performance resulting in higher or lower mechanical efficiency of locomotion. Given the sport's popularity and significance of technical proficiency for both safe participation (Sherker and Cassell, 2002) and competitive performance (Parrington et al., 2013), it is surprising that studies evaluating specific skating skills are scarce. In order to optimize training, the contribution of generic motor abilities and specific skills in performance should be quantified and continuously monitored (Coutts and Cormack, 2004; Smith, 2003). While the literature offers a range of accepted methods for assessing generic motor abilities (Reiman and Manske, 2009), reproducible methods for testing specific skill in inline skaters are lacking. Our investigation aimed to examine the inter-session reliability and test the validity of the inline skating skill test in amateur skaters. Due to the mass popularity of roller sports, we performed the study on amateur inline skaters with the intention to aid coaches and skaters evaluate specific skater skills.
The study design encompassed two separate sections: the first evaluated the inline skating skill test's reliability, and the second assessed the test's validity. The test-retest reliability was evaluated comparing inline skaters' mean performances during subsequent skating sessions. The second measurement property--the construct validity was in exercise science considered to be the extent to which a test discriminates between individuals of different standards (Ali et al., 2007). Therefore, the discriminative ability, and to an extent the construct validity of the proposed test, was examined comparing test outcomes of two groups categorized by different inline skating experience (amateur competitive vs. amateur recreational). Experience has already been identified as a good predictor of stride efficiency in inline skating performance (Parrington et al., 2013), hence it is a valid criteria for standard categorization. In order to add the discriminatory value and to supplement the hypothesis about the test's construct validity, individual test outcomes were correlated with the participants' inline skating skill self-ratings. This is a rational approach since some authors report that study participants can accurately evaluate their motor abilities (Sporis et al., 2011). The participants in the study, the inline skating skill test, as well as the experimental procedure and statistical analysis are described in detail in the next subsections.
Forty-two adult female and male subjects who have been skating for at least two years were invited and volunteered in the study. All skaters, 26 female (age 23.3 [+ or -] 6.5 yrs, height 1.69 [+ or -] 0.07 cm, body mass 63.0 [+ or -] 6.5 kg) and 16 male (age 24.7 [+ or -] 10.0 yrs, height 1.78 [+ or -] 0.06 m; body mass 77.2 [+ or -] 9.9 kg) were recruited from the local skating association. They were members of an inline skating club or inline hockey club, which regularly participated in national amateur competitions. However, while some skaters participated both in training and in amateur competitions, others did not compete but regularly participated in training for health reasons, as described by Kokko et al. (2009). All skaters were interviewed before the study in order to check their eligibility, to establish two qualitative groups, and to ensure gender balance in both categories. During the interview they were asked about their skating experience and whether they had participated in competitions. Based on their responses, skaters were allocated to either competitive-level group (>2 years of amateur competition experience) or recreational-level group (no competition experience). Both groups had a similar distribution of males and females (~60% female vs. ~40% male) and did not differ in their sprint/agility performance. Inclusion criteria included at least 2 years of roller training experience, at least once weekly, the absence of illness, and no recent injury. The study was approved by the Ethics Committee of the University of Zagreb, School of Kinesiology. Each subject was individually informed about the nature, purpose and potential risks of the study, and written consent was obtained in compliance with the Declaration of Helsinki.
The Inline Skating Skill Test
The test was constructed to evaluate the individual's inline skating skill. It included techniques typical for roller sports such as start, circling and S-turning, push-off technique, acceleration, direction changes, and parallel technique. The following components of skills were tested: efficiency of pushing technique, coordinated direction changes and speed save. Thus, the performance time was used as an outcome measure of the evaluated inline skating test. The 83 m long testing course consisted of two tasks involving skating in 360[degrees] circles around markers (cones), three long accelerations using the push-off technique and each of those followed by parallel skating through the four cones positioned for slalom. As depicted in Figure 1, the goal was to skate the skating...