Abstract
al requirements are necessary to maintain the entire body in a streamlined and aerodynamic position during downhill skiing. Balance control has an important role in alpine skiing and depends on muscle endurance and strength. The central processing of proprioception and the force capacity of muscle are altered by fatigue. The objective of this study was to assess the effects of fatigue and visual input on balance control in alpine skiing. Methods: Eleven male professional skiers participated in the study. Balance control with eyes open and eyes closed was assessed before and after performing a maximal effort specific alpine ski test. Variables: the total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit time)
participated in the study. Balance control with eyes open and eyes closed was assessed before and after performing a maximal effort specific alpine ski test. Variables: the total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit time) (mm/s), the mean mediolateral (ML) COP oscillation velocity (Lat_Vel) (mm/s), the mean anteroposterior (AP) COP oscillation velocity (AP_Vel) (mm/s), mean ML (MLD) (mm) and mean AP (APD) (mm) displacements of the COP and the distance from the ordinate origin (mean X and mean Y) (theoretical point where the COP should be) to the point at which the COP is located, and heart rate were measured. Results: The results showed differences in the variables related to postural control and balance before and after the stress test (p= 0.002–0.037).However, no differences were found when the results obtained with open and closed eyes were compared. Conclusions: The results showed that performance in alpine skiing could be negatively affected by fatigue. However, the dynamic parameters are not decreased by visual input during muscle fatigue. Keywords:ski; balance control; postural balance; fatigue; maximum effort 1. Introduction Alpine skiing has been one of the Winter Olympic sports since 1936. There are four main types of alpine skiing events (downhill, super giant slalom, giant slalom, and slalom), and these events are approximately 90 s to 2 min in duration. The skier has to accelerate as quickly as possible and to maintain correct form and technique from the starting gate to the remainder of the race [1]. Alpine skiing is an outdoor winter sport where balance control, Life2025,15, 679 https://doi.org/10.3390/life15050679
Life2025,15, 679 2 of 10 weight transfer skills, isometric muscle strength in the lower extremities, mainly gravity, postural performance, coordination, and anaerobic–aerobic performance are required [2]. Among the variables, the effectiveness of the ride is largely determined by the balance [3,4]. During downhill skiing, static posture toward the skis is kept by the skier, as well as to maintain the balance of the entire “man-skis” relative to the ground, and its center of mass must project onto the base of support [4,5]. Modern alpine skiing techniques are characterized by a strong sense of lateral and forward–backward balance due to the wide angles of the inward lean of the body [3]. Therefore, great physical requirements are necessary to maintain the entire body in a streamlined and aerodynamic position or to make short radius turns during downhill skiing. Static and dynamic balance in humans is regulated by a complex system of organs and mechanisms including the visual, vestibular, and somatosensory systems [6]. During ski turns, the share of vestibular information in posture control is increased by modifications in angular and linear acceleration; similarly, the afferent impulses from sight rise by the constant shift in space [6,7]. Therefore, skiing could be considered as a demanding sport because some studies have shown that attentional demands are greater for unstable than for stable balance conditions [8,9]. Sight plays a fundamental role in skiing, providing significant information related to body displacement kinematics, speed, and direction [10]. Research has shown a close relationship between dynamic balance and performance. Therefore, alpine ski training should be tailored to develop balance [10]. However, one variable that has not yet been explored in depth is the fatigue during downhill skiing. In this regard, balance control depends on muscle endurance and strength in developing postural control [11,12]. The central processing of proprioception and the force capacity of muscle are altered by fatigue, involving neural and muscular mecha- nisms [13–15]. This balance control largely depends on the proprioceptive input from the muscles of the legs and trunk [16]. It is known that proprioception is negatively affected by muscle fatigue. There has been some
in developing postural control [11,12]. The central processing of proprioception and the force capacity of muscle are altered by fatigue, involving neural and muscular mecha- nisms [13–15]. This balance control largely depends on the proprioceptive input from the muscles of the legs and trunk [16]. It is known that proprioception is negatively affected by muscle fatigue. There has been some investigation into the role of proprioception in balance control, which has shown how increased local fatigue of the lower limbs decreases balance control [17–19]. Furthermore, balance control is more negatively affected by the fatigue of the proximal muscles of the lower limbs compared to distal muscles [18]. In alpine skiing, previous research has shown a high level of effort by knee extensor muscles during skiing [20,21]. Therefore, this should mean that performance should be seriously affected by the fatigue of the lower limbs. Increasing fatigue is an important variable related to the balance control of an alpine skiing athlete, which can lead to lower performance. Unlike previous studies, the acute effects of fatigue on balance have not been studied previously in depth. Therefore, analysis enables researchers and coaches to align the actual performance used during training sessions with the scheduled load based on the level of fatigue based on balance. This makes the control of fatigue particularly useful to know the effects of the fatigue on physical performance. Although balance control plays an important role in alpine skiing, most studies have focused on physiology, biomechanics, and injuries. Few studies have evaluated the acute effects of fatigue on balance control [18,22,23]. Therefore, the main objective of the present study was to determine how balance control could be affected by muscle fatigue and visual input after performing a maximal effort alpine skiing test. Based on the previous literature, it was hypothesized that a high level of fatigue would lead to the decreased performance of alpine athletes.
Life2025,15, 679 3 of 10 2. Materials and Methods 2.1. Participants The study sample consisted of 11 male skiers (age: 23.8±7.4 years; height: 177±3.1 cm; body mass: 73.3±2.3 kg) who were working as alpine ski instructors at the time the investigation was carried out. All subjects had uninterrupted experience practicing skiing for more than 10 years. The inclusion criteria of this sample were to ensure that skiers can perform the task accurately and to have a homogeneous sample. The participants had no physical limitations, health problems, or musculoskeletal injuries that could affect the evaluation. The measurements protocol performed are presented in Figure.Life 2025, 15, x FOR PEER REVIEW 3 of 10 The study sample consisted of 11 male skiers (age: 23.8 ± 7.4 years; height: 177 ± 3.1 cm; body mass: 73.3 ± 2.3 kg) who were working as alpine ski instructors at the time the investigation was carried out. All subjects had uninterrupted experience practicing skiing for more than 10 years. The inclusion criteria of this sample were to ensure that skiers can perform the task accurately and to have a homogeneous sample. The participants had no physical limitations, health problems, or musculoskeletal injuries that could affect the evaluation. The measurements protocol performed are presented in Figure 1. Figure 1. Flowchart of the experimental setup. All participants were informed in a briefing about the purpose and methods of the study, as well as their right to withdraw at any time. All our procedures complied with the Helsinki Declaration, which outlines ethical principles for research involving humans. The study was approved by the CEIm Hospital Clínico San Carlos (identification code: 22/576-E) Ethics Committee in Madrid (Spain). 2.2. Materials The Podoprint ® platform was used (Podoprint v2.6, Namrol Group, Barcelona, Spain) to asses postural sway [24,25]. The total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit time) (mm/s), the mean mediolateral (ML) COP oscillation velocity (Lat_Vel) (mm/s), the mean anteroposterior (AP) COP oscillation velocity (AP_Vel) (mm/s), mean ML
to asses postural sway [24,25]. The total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit time) (mm/s), the mean mediolateral (ML) COP oscillation velocity (Lat_Vel) (mm/s), the mean anteroposterior (AP) COP oscillation velocity (AP_Vel) (mm/s), mean ML (MLD) (mm), and mean AP (APD) (mm) displace- ments of the COP and the distance from the ordinate origin (mean X and mean Y) (theo- retical point where the COP should be) to the point at which the COP is located were measured at a frequency of 100 Hz, using the manufacturer’s specific software [24,25]. The heart rate was recorded with a heart rate monitor (Polar Electro RS800cx, Kempele, Fin- land). 2.3. Balance Control Test This was the first test that the subjects had to carry out. Before the measurements, the participants were informed about the entire process and the protocol for standing on the platform [26,27]. Participants were instructed to stand erect with their feet width the same as their shoulder width on the platform without shoes, motionless, and with their hands on their hips. They had to remain still in that position for 30 s while the measurements were made. Subsequently, a second measurement was taken in the same posture with eyes closed, within 30 s. 2.4. Maximal Effort Test Figure 1.Flowchart of the experimental setup. All participants were informed in a briefing about the purpose and methods of the study, as well as their right to withdraw at any time. All our procedures complied with the Helsinki Declaration, which outlines ethical principles for research involving humans. The study was approved by the CEIm Hospital Clínico San Carlos (identification code: 22/576-E) Ethics Committee in Madrid (Spain). 2.2. Materials The Podoprint ® platform was used (Podoprint v2.6, Namrol Group, Barcelona, Spain) to asses postural sway [24,25]. The total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit
(identification code: 22/576-E) Ethics Committee in Madrid (Spain). 2.2. Materials The Podoprint ® platform was used (Podoprint v2.6, Namrol Group, Barcelona, Spain) to asses postural sway [24,25]. The total travel distance (TTD) (mm), radial area (RA) (mm 2 ), ratio between TTD and RA (TTD/RA) (1/mm), mean center of pressure (COP) velocity (total length of the COP path per unit time) (mm/s), the mean mediolateral (ML) COP oscillation velocity (Lat_Vel) (mm/s), the mean anteroposterior (AP) COP oscillation velocity (AP_Vel) (mm/s), mean ML (MLD) (mm), and mean AP (APD) (mm) displacements of the COP and the distance from the ordinate origin (mean X and mean Y) (theoretical point where the COP should be) to the point at which the COP is located were measured at a frequency of 100 Hz, using the manufacturer’s specific software [24,25]. The heart rate was recorded with a heart rate monitor (Polar Electro RS800cx, Kempele, Finland). 2.3. Balance Control Test This was the first test that the subjects had to carry out. Before the measurements, the participants were informed about the entire process and the protocol for standing on the platform [26,27]. Participants were instructed to stand erect with their feet width the same as their shoulder width on the platform without shoes, motionless, and with their hands on their hips. They had to remain still in that position for 30 s while the measurements
Life2025,15, 679 4 of 10 were made. Subsequently, a second measurement was taken in the same posture with eyes closed, within 30 s. 2.4. Maximal Effort Test After completing the warm-up (5 min of jogging, 2 sets of 10 squats without additional load, 2 sets of 10 squats without additional load with ski, ski steps, several sets of progres- sively faster running accelerations with ski), participants performed an interval test, which consisted of a maximum-speed ski descent for 200 m (25% slope), with turning gates every 10 m. Upon reaching the end of the ski slope, they carried their skis on their shoulders and returned to the starting point. They had a maximum of 3 min to return to the starting point, put on their skis, and make a new descent. The test ended when two criteria were met: subjective exhaustion (modified 0–10 Borg scale (value 10 recorded)) and reaching at least 85% of the theoretical maximum heart rate [28,29]. Immediately, at the end of the interval-type test, the subjects returned to perform a second assessment of balance control with eyes open and closed, following the same protocol as in the initial assessment. 2.5. Statistical Analyses Data are presented as the mean (M)±standard deviation (SD). The normal distribu- tion of data was confirmed using the Shapiro–Wilk’s test, and Leven’s test revealed the homogeneity of variance. A two-way repeated-measures ANOVA was used to analyze the effects of eye condition (open and closed) and time (pre-fatigue and post-fatigue) on the variables related to lengths, surface areas, velocities, and variations in the center of gravity. When a significant main effect was detected, pairwise comparisons were assessed using the Holm–Bonferroni test. Furthermore, ANOVA-RM effect sizes (ESs) were calculated using partial eta squared (ηp 2), with values <0.25, 0.26–0.63, and >0.63 considered small, medium, and large effect sizes, respectively [30,31]. On the other hand, in the pairwise comparisons, significance was assessed by calculating Cohen’s d ES [31]. Effect sizes were categorized as large (>0.8), moderate (0.5–0.8), small (0.2–0.5), and trivial (<0.2) [30,31]. Statistical significance was set atp< 0.05. All the statistical tests were performed using
with values <0.25, 0.26–0.63, and >0.63 considered small, medium, and large effect sizes, respectively [30,31]. On the other hand, in the pairwise comparisons, significance was assessed by calculating Cohen’s d ES [31]. Effect sizes were categorized as large (>0.8), moderate (0.5–0.8), small (0.2–0.5), and trivial (<0.2) [30,31]. Statistical significance was set atp< 0.05. All the statistical tests were performed using SPSS (version 18.0; SPSS, Chicago, IL, USA). 3. Results Table fatigue conditions. TTDshowed statistically significant differences between pre- and post-fatigue conditions (86.8±20.2 vs. 245.5±38.5 mm;p= 0.002;ηp 2= 0.633) for both open (p= 0.010; ES = 1.30) and closed eyes (p= 0.030; ES = 1.08). RA showed a trend towards statistical significance with higher values in the post-fatigue condition (149.4±58.6 vs. 1319.5±526.5 mm 2 ;p= 0.054;ηp 2= 0.322). The TTD/RA showed significant differences between the pre- and post-fatigue conditions, with a lower value in post-fatigue (1.54±0.26 vs. 1.48±0.26; 1/mm;p= 0.001;ηp 2= 0.692). These significant differences were found for both open (p= 0.005; ES = 0.06) and closed eyes (p= 0.014; ES = 0.07). However, no significant differences were found between eye conditions or the interaction time and eye condition for TTD, RA, or TTD/RA (p> 0.05).
Life2025,15, 679 5 of 10 Table 1.The stabilometry and baropodometry platform values pre- and post-fatigue. Variable Eyes Time p-Value Time ηp 2 Time p-Value Eye ηp 2 Eye p-Value Eye·Time ηp 2 Time·EyePre-Fatigue Post-Fatigue TTD (mm) Open 94.5±83.0 * A 274.5±188.3 0.002 * 0.633 0.386 0.076 0.607 0.027 Closed 79.1±55.8 * B 216.4±179.3 RA (mm 2 ) Open 187.3 ±321.7 1725.8±3139.0 0.054 0.322 0.467 0.054 0.545 0.038 Closed 111.4 ±84.7 913.2±1952.3 TTD/RA (1/mm) Open 1.31±0.94 * A 1.26±0.91 0.001 * 0.692 0.192 0.164 0.412 0.068 Closed 1.77±1.05 * B 1.70±1.08 Data presented as M±SD. TTD: Total travel distance; RA: radial area; TTD/RA: ratio between total travel distance and radial area; Significant differences for the time factor atp< 0.05. *: Significant difference be- tween pre- and post-fatigue conditions; * A : Significant difference between pre- and post-fatigue with open eyes; * B : Significant difference between pre- and post-fatigue with closed eyes; TTD/RA: ratio between total travel distance and radial area. Table control test. For the velocity variables, no differences were observed between open and closed eyes for the interaction of time and eye condition (p> 0.05). A significant difference was found for the mean velocity with open eyes in the post-fatigue situation (p= 0.031; ES = 1.02), but no significant changes were observed for closed eyes in the post-fatigue situation (6.67±1.31 vs. 2.78±0.57 mm/s;p= 0.011;ηp 2= 0.489). In Lat_Vel, higher values in the post-fatigue than the pre-fatigue condition were detected (4.70±1.07 vs. 1.91±0.42 mm/s;p= 0.003;ηp 2= 0.399). A significant increase in AP_Vel in the post-fatigue condition was also detected (4.53±0.86 vs. 1.91±0.39 mm/s;p= 0.006; ηp 2= 0.551), including these statistical differences with open eyes (p= 0.008; ES = 1.15) and a trend to statistical significance in closed eyes (p= 0.056; ES = 0.89). Table 2.Values of the variation of the velocity of the center of mass in the balance control test. Variable Eyes Time p-Value Time ηp 2 Time p-Value Eye ηp 2 Eye p-Value Eye·Time ηp 2 Time Eye Pre-Fatigue Post-Fatigue Mean velocity (mm/s) Open 2.93±2.39 * A 7.55±6.28 0.011 * 0.489 0.428 0.064 0.563 0.035 Closed 2.65 ±1.54
ES = 0.89). Table 2.Values of the variation of the velocity of the center of mass in the balance control test. Variable Eyes Time p-Value Time ηp 2 Time p-Value Eye ηp 2 Eye p-Value Eye·Time ηp 2 Time Eye Pre-Fatigue Post-Fatigue Mean velocity (mm/s) Open 2.93±2.39 * A 7.55±6.28 0.011 * 0.489 0.428 0.064 0.563 0.035 Closed 2.65 ±1.54 5.79 ±5.60 Lat_Vel (mm/s) Open 2.07 ±1.83 5.65 ±5.71 0.028 * 0.399 0.325 0.097 0.471 0.053 Closed 1.75 ±1.08 3.71 ±4.23 AP_Vel (mm/s) Open 2.01±1.57 * A 4.84±3.31 0.006 * 0.551 0.558 0.035 0.746 0.011 Closed 1.81 ±1.13 4.21 ±3.83 Data presented like M±SD. Mean velocity: mean center of pressure (COP) velocity (total length of the COP path per unit time); Lat_Vel: the mean mediolateral (ML) COP oscillation velocity; the mean anteroposterior (AP) COP oscillation velocity; significant differences in factor time atp< 0.05. *: Significant difference between pre- and post-fatigue conditions; * A : significant difference between pre- and post-fatigue with open eyes. Table relation with MLD, significant differences between the pre- and post-fatigue conditions were observed (1.69±0.32 vs. 4.00±0.98 mm;p= 0.037;ηp 2= 0.368), with the statistical significances observed only with the open eye condition (p= 0.044; ES = 2.84), with no differences for eyes (p= 0.589) or the interaction time·eye (p= 0.892). On the other hand, in APD, differences were not observed for the factors time (p= 0.060), eye (p= 0.854), or the time·eye interaction (p= 0.423).
Life2025,15, 679 6 of 10 Table 3.Values of the variation of the position of the center of mass in the balance control test. VariableEyes Time p-Value Time ηp 2 Eye p-Value Eye ηp 2 Time p-Value Eye·Time ηp 2 Eye·TimePre-Fatigue Post-Fatigue MLD (mm) Open 1.92±0.45 * A 4.37±1.20 0.037 * 0.368 0.589 0.030 0.892 0.002 Closed 1.45±0.23 3.63±1.59 APD (mm) Open 2.75 ±1.95 4.12±2.46 0.060 0.311 0.854 0.004 0.423 0.065 Closed 2.21±1.63 4.95±5.06 Data presented like M±SD. MLD: mean mediolateral displacements of the COP and the distance from the ordinate origin (mean X and mean Y) (theoretical point where the COP should be) to the point at which the COP is located; APD: mean anteroposterior displacements of the COP and the distance from the ordinate origin (mean X and mean Y) (theoretical point where the COP should be) to the point at which the COP is located; significant differences in factor time atp< 0.05. *: Significant difference between pre- and post-fatigue conditions; * A : significant difference between pre- and post-fatigue with open eyes. 4. Discussion The purpose of this study, which has been achieved, was to determine how balance control could be affected by muscle fatigue and visual input after performing a maximal effort alpine skiing test. The hypothesis planned was accepted, since it was a high level of fatigue that led to decreased performance regarding the balance of an alpine athlete. In the present study, the postural sway assessment showed significant differences between pre-exercise and post-exercise with eyes open and eyes closed. These differences were observed both in dynamic and static parameters with eyes open and in dynamic parameters with eyes closed. Our results suggest that it could be considered that balance control could be affected by muscle fatigue. Studies focused on changes in balance control with fatigue indicated that postural stability in either the sagittal or frontal planes have a greater deterioration when the proximal musculature of the lower limbs is fatigued [20]. Alpine skiing is characterized essentially by turns and this technical gesture, which demand greater sagittal balance where the proximal hip musculature is involved in
Description
This study evaluates how fatigue affects balance control in alpine skiing athletes.