INTRODUCTION

Inline speed skating is a sport that has been gaining fans over the years and received many athletes at the last world competitions. However, scientific knowledge regarding the sport is still limited (^{Stangier et al., 2016a}). The athletes must be fast, maintain muscle power, and show a high aerobic capacity to achieve competitive success (^{Stangier et al., 2016a}; ^2016b). However, the analysis of specific characteristics regarding their specialized sport could help training prescriptions because a sprinting competition lasts approximately 16-18 seconds (200 m). In contrast, a marathon lasts between 60-70 min (^{Stangier et al., 2016b}). Despite limited specific scientific literature regarding this sport, some authors have indicated that physiological, biomechanical (^{Wu, Hsu, Chu, Tsai, & Liang, 2017}), and anthropometric measures (^{Knechtle, Knechtle, Rüst, Rosemann, & Lepers, 2012}) can determine competitive success in ISS.

Foster et al. (¹⁹⁹⁹) showed that aerobic capacity alone does not determine competitive success in ISS, requiring specific strength work on the lower limbs to improve competitive performance (^{Juda, Yuki, Aoyanagi, Fujii, & Ae, 2007}; ^{Piucco, Santos, & Lucas, 2014}; ^{Stangier et al., 2016a}, ^2016b). Besides, higher strength levels enhance technical performance and result in competitive advantage (^{Yugay, 2015}). Despite the importance of strength for ISS performance, few studies have investigated this variable, and the protocols did not measure power in the athletes of this sport (^{Piucco et al., 2014}).

Among the methods used to measure strength, the Isometric Mid-Thigh Pull Test (IMTP) is valid and is potentially accurate (^{De Witt et al., 2018}) for assessing maximal force (^{Dos’Santos et al., 2019}). The peak force (PF) variable is a practical and more effective test than the 1-MR test (^{Townsend et al., 2019}). Furthermore, the PF measured by the IMTP has been correlated (r = 0.704) with the sprinting ability (^{Townsend et al., 2019}) and agility (r = -0.854) in other sports (^{Spiteri et al., 2014}). However, to the best of our knowledge, no study has measured this variable in ISS. It is unknown what variables determine the PF in this group of athletes or gender differences. The results presented in this study can help coaches build specific and contextualized programs for athletes of this sport and learn which physical measure can predict PF in cadet ISS athletes. Therefore, the present study aimed to a) measure the PF in male and female cadet ISS athletes; and b) verify the physical measures which determine the performance of cadet ISS athletes on the IMTP through a multivariate regression and discriminant canonical analysis. We hypothesize that anthropometric measurements can determine the IMTP.

METHODS

This study employed a test-retest design in which all participants performed two testing sessions separated by three days to analyze reliability and the impact of anthropometric characteristics and low-back and hamstring flexibility on the PF registered with the IMTP. The sit-and-reach test (SR) assessed flexibility, and the present study measure anthropometric variables: height, body mass, thigh, and calf circumference. Figure 1 shows the data collection chart.

Figure 1. Chart of procedures and data collection. 

Isometric Mid-Thigh Pull test

The IMTP was used to assess lower-limb maximal PF. This test was performed on two portable force plates (type= PS-2142; sampling= 50-1,000 Hz; Range= -1,000 to 4,400 N over 6,600 N; Resolution= 0.34 N; dimensions= 350 mm × 350 mm, PASCO^® Instrument Inc., USA) which were placed on a portable IMTP rack where the bar height could be adjusted (4 cm increments) at various heights above the force plate to adjust to each participant’s height (^{Peterson Silveira et al., 2017}). The sampling was set at 1,000 Hz since it has shown good reliability in force-time variables (^{Dos’Santos et al., 2019}). The initial position was individualized to each athlete, grasping the barbell straight but with arms relaxed, setting the barbell at their mid-thigh height with a hip flexion angle between 140-145° and knee flexion angle between 125-145º while maintaining the trunk upright (^{Drake, Kennedy, & Wallace, 2017}).

The athletes performed a warm-up and familiarization with the IMTP test before testing, which was divided into three phases: general warm-up, dynamic warm-up, and specific warm-up, according to (^{Comfort et al., 2019}). All athletes received standard instructions for the test, which was to pull “as fast and hard as possible and push their feet directly into the force plate” (^{Halperin, Williams, Martin, & Chapman, 2016}). A minimal pre-tension was allowed before they started (< 50 newtons above their body weight) to ensure there was no slack in the body before the first pull (^{Comfort et al., 2019}). Once the body position was verified, the test was started with the sign of “3, 2, 1, pull,” and maintaining the maximal effort for five seconds. They were verbally encouraged during the test to enhance the maximal effort. Figure 2 shows the correct starting position for performing the IMTP.

Figure 2. Starting position to perform the Isometric Mid-Thigh Pull test (IMTP). 

The present research examined the reliability of IMTP, verifying the association between a test and retest with three days between them (^{Drake et al., 2017}). The intraclass correlation coefficient (ICC) and Pearson correlation verified the association between the test and retest. The coefficients assume values between -1 and 1, as the closer, it gets to 1, the more concordance will exist between tests for IMTP. Correlation analysis indicated a strong correlation between the IMTP test and retest (r = 0.84, IC = 0.95, p ≤ 0.001).

Experienced analysts collected the vertical ground reaction force data during ten seconds of each trial using the Capstone 2.0 program (Pasco company, California, United States). After that, researchers calculated the PF and normalized to athletes’ body mass, using the MATLAB (MathWorks^®, Inc., Natick, Massachusetts, United States). The athletes performed two trials with a 3-minute interval. The present research uses the best result between the two attempts for the analyzes. A cut-off point of intraclass correlation coefficient (ICC = ≥ 0.7, p ≤ 0.001) between test and retest was used for internal validation as maximum effort performed, as suggested by Drake et al. (²⁰¹⁷). Those with ICC< 0.7 repeated the tests on another day.

RESULTS

Analysis indicated a significant and moderate correlation between the IMTP with Thigh circumference (r = 0.52, p ≤ 0.001) and Calf circumference (r = 0.42, p = 0.011). Table 1 shows the descriptive and inferential analysis of IMTP performance in male and female cadet ISS athletes.

The multivariate logistic regression analysis of IMTP performance in male and female cadet ISS athletes was composed of four steps. We only included significant models in the results. The first model used thigh circumference (χ² = 29.01, p ≤ 0.001, R2 = 0.74) and had an overall prediction of 91.7% (88.9% male and 94.4% for female). The second model included showed the SR test and thigh circumference (χ² = 49.91, p ≤ 0.001, R2 = 1.0) as prediction variables with an overall prediction of 100% (100% male and female). Table 2 shows the significant models obtained by the multivariate logistic regression analysis.

Table 3 shows the matrix correlations between the anthropometry and physical tests and canonical coefficients. The main matrices showed a better predictive power for thigh circumference (coefficient= 7.158), as this measurement showed a higher predicting value for the models presented in Table 2.

DISCUSSION

The IMTP measures the PF, and the results of this test are associated with sprinting (^{Brady, Harrison, Flanagan, Haff, & Comyns, 2019}) and lower limb agility performance (^{Thomas, Comfort, Jones, & Dos’Santos, 2017}). Thus, we believe that the IMTP can be a good predictor of performance in ISS. However, to the best of our knowledge, no studies have been performed using this measure in male and female ISS athletes. The present study measured the PF in cadet ISS athletes and performed an analysis to learn the physical tests which determine the IMTP performance in cadet ISS athletes. The main results indicated significant differences between female and male athletes for all variables, except for the SR. A multivariate logistic regression analysis revealed thigh circumference as the main factor in predicting gender differences of IMTP performance in cadet ISS athletes, differentiating male and female groups. The strength levels are directly related to this sport (^{Stangier et al., 2016a}, ^2016b), mainly of the thigh and gluteus muscles (^{Stangier et al., 2016b}). To the best of our knowledge, this is the first study to measure IMTP in ISS athletes. Our results showed an anthropometric performance predictor (thigh circumference), which can be monitored by coaches. We emphasize that there is a limitation in our study regarding the use of our results. We did not measure competitive performance. However, the PF is a performance indicator in sports that require speed (^{Brady et al., 2019}), agility, strength (^{Thomas et al., 2017}; ^{De Witt et al., 2018}; ^{Townsend et al., 2019}), and muscle power (^{Townsend et al., 2019}).

Furthermore, in sports for which the ability to sprint is a differential in the athlete’s performance (^{Beckham et al., 2013}; ^{Brady et al., 2019}), such as rugby, weightlifters (^{Beckham et al., 2013}), and sprint cycling (^{Stone et al., 2004}), PF has proven to be able to differentiate athletes regarding the competitive level. Stone et al. (²⁰⁰⁴) observed that the strongest athletes in cyclists of the national team had significantly higher PF (4,590± 314 vs. 2,551± 466 N) compared to the weakest, and the faster athletes also showed a significant difference (4,164± 803 vs. 2,795± 528 N) versus the slowest. Through these results, we believe that ISS athletes can also have a direct relationship between performance level and PF in IMTP.

Previous studies in ISS have directed attention to biomechanical and anthropometric indicators, determining the performance (^{Knechtle et al., 2012}; ^{Stangier et al., 2016b}). Juda et al. (²⁰⁰⁷) demonstrated a relationship between technical aspects and the increase of aerodynamics. In contrast, findings indicated that plantar pressure could determine the foot and ankle’s best angle, which results in increased speed (^{Wu et al., 2017}). Anthropometric measures (^{Knechtle, Knechtle, Rosemann, & Lepers, 2010}) in ISS athletes observed that the leg’s height and length (r = 0.61 for both variables) have a direct association with the competitive performance. However, another study by the same group of researchers indicated that anthropometric variables could not predict ISS (^{Knechtle et al., 2012}). The present research suggests further investigations about the relationship between ISS specific movements and IMTP performance, considering female and male athletes.

Few studies have observed the predictive capacity of anthropometric indicators and the PF in IMTP. McMahon, Stapley, Suchomel, and Comfort (²⁰¹⁵) observed that the thickness of the dominant leg’s vastus lateralis in male college athletes is directly related to the performance in IMTP (R ² = 0.38). In this same line, Secomb et al. (²⁰¹⁵) observed a correlation between IMTP and vastus lateralis thickness (R ² = 0.45), vastus lateralis pennation angle (R ² = 0.21), and lateral gastrocnemius (R ² = 0.29) in adolescent surfers (male and female). An increased pennation and thickness of vastus lateralis enable higher lower limb strength and muscle power. There will be a higher number of sarcomeres and cross-bridges, which increases muscle strength (^{Secomb et al., 2015}).

Still, regarding the prediction models, the second significant variable (Table 2) showed that the sit-and-reach test associated with the thigh circumference could increase the prediction for IMTP, regardless of gender. Studies have shown that the hamstrings’ flexibility levels can increase or decrease the lower limb power (^{Aguilar et al., 2012}; ^{Medeiros, Cini, Sbruzzi, & Lima, 2016}) because the shortening affects the quadriceps extensibility (^{Aguilar et al., 2012}). As hamstrings are a muscle that is favourable to shortening, coaches must monitor this measurement. Besides, there is a higher risk of injury in athletes with hamstring shortening (^{Medeiros et al., 2016}). Our results indicated no differences between genders, but the means were lower than those observed in other elite athletes (^{Aedo-Muñoz et al., 2019}).

The calf circumference was not predictive in any model. In contrast, Mishra and Chahal (²⁰¹³) analysis indicated a positive correlation (r = 0.48) between calf circumference and lower limb power in male throwers. Among the limitations of the present study is the absence of direct performance in ISS competition and the lack of analysis separated in a sprinter and long-distance ISS athletes. Future studies can measure how IMTP can predict competition performance. Furthermore, the progress of ISS science can help coaches of other sports, since even though the characteristics of ISS are not entirely transferable (^{Piucco et al., 2014}), it can be a training alternative for skiing athletes in seasons without snow (^{Piucco et al., 2014}; ^{Stangier et al., 2016b}).

CONCLUSIONS

Based on our aims, methods, and results, we can conclude those male athletes showed a higher PF and thigh circumference as the main factors to predict gender differences of IMTP performance in cadet ISS athletes.