In the last decade, the popularity of snowboarding has increased dramatically, becoming one of the premier alpine winter sports (3). Snowboarding comprises 3 different disciplines: freestyle, alpine, and snowboard cross. Of these, in alpine snowboarding (ALP), 2 athletes ride simultaneously side-by-side down 2 parallel courses through gates with tight turns. The setting of the courses, the configuration of the terrain, and the preparation of the snow are identical. Each run lasts approximately 30–45 seconds and 10 runs must be won to obtain the victory. One of the key features is that ALP, as the other snowboarding disciplines, is a sport in which an athlete is fixed to the board with the left or the right leg in front (regular or goofy position, respectively). Recently, it has been shown that muscle strength asymmetry exists between the front leg (FL) and the rear leg (RL) of elite ALP athletes, and this characteristic may predispose the snowboarders to future musculoskeletal injuries in the lower limbs (34).
Muscle architecture refers to the arrangement of the muscle fibers with respect to the muscle's axis of force generation (23). For instance, increases in fiber angle are thought to improve the force-generating capacity of a muscle by allowing a greater muscle mass to attach to a given area of tendon (21). Therefore, muscle architecture is one of the factors most strongly affecting the skeletal muscle's contractile properties (23). To our knowledge, only 3 studies have previously reported acute adaptations in quadricep muscle architecture after dynamic exercises. Brancaccio et al. (6) determined whether or not an incremental cycle ergometer test to exhaustion induced changes in the intramuscular architecture of the quadriceps in trained athletes. The authors showed marked changes in intramuscular architecture of the quadriceps with a significant increase of quadricep thickness (∼9%) and pennation angle (∼12.5%). Csapo et al. (9) assessed acute changes in muscle architecture after induction of fatigue by a leg press exercise, showing that the vastus lateralis (VL) muscle thickness (MT) and pennation angles increased by ∼7 and ∼10%, respectively, with a concomitant ∼2% decrease in the fascicle lengths. Finally, Kubo et al. (22) investigated the effects of knee extension tasks with 4 different contraction modes on the muscle architecture properties. Results showed that VL MT and pennation angles significantly increased after each knee extension tasks. Together, these studies suggest that quadricep muscle architecture is negatively affected by previously performed bouts of exercise.
Over the years, several studies focused the attention on the risk of injuries in ALP (1,3,10,15,31). However, to the best of our knowledge, no data on muscle architecture are present. The understanding of its acute changes after an ALP race might allow for insights into these mechanisms, deepening our understanding of the intramuscular processes involved during an ALP race and providing a rationale for injury prevention and training prescription/adaptations.
Therefore, this study aimed to assess acute changes of VL muscle architecture, as representative of the whole quadricep muscles (4,27), to elucidate the muscular reactions to an ALP simulated race. Furthermore, a second aim was to compare architecture characteristics in VL of front and rear legs.
Experimental Approach to the Problem
A longitudinal, quasi-experimental design was used for this study, which was conducted during the competitive season. The day before (PRE) and immediately after (POST) an ALP simulated race, muscle architecture assessments were made using ultrasound. Measurements were taken in an indoor room, close to the ski slope, where the temperature was relatively constant at approximately 20° C. Based on previous studies showing that time course of changes in muscle architecture restored within 15 minutes (9), time interval between the end of the ALP simulated race and POST measurements was <10 minutes. All measurements were randomly performed on the VL muscle of both the FL and RL. Test order was randomized among athletes at PRE and repeated in the same order at POST.
Participants were 8 snowboarding (mean ± SD age: 25.6 ± 4.4 years; stature: 178.4 ± 9.8 cm; body mass: 78.1 ± 12.1 kg; body mass index: 24.4 ± 2.5) members of the Italian National ALP Snowboard Team A, who competed internationally in International Ski Federation World Cup and Europa Cup events. Athletes who have had any injuries to the lower extremities within 6 months before the start of the study and have not completed a standard rehabilitation program were excluded. All the athletes gave written informed consent to participate in the study, which had received approval from the institutional research ethics committee and was laid out according to the Declaration of Helsinki.
Athletes lay in a supine position on an examination bed with their knees in the anatomical position (0°). By means of a real-time B-mode ultrasonography with a 5-cm, 7.5-MHz linear-array ultrasound probe (AU5 Harmonic, Esaote Biomedica, Genoa, Italy), 3 images were taken on the center of VL muscle belly using sagittal-plane ultrasound scans, halfway between the lateral epicondyle of the knee and the greater trochanter. The site was clearly marked on the skin with indelible ink and further outlined on tracing paper, to provide a standardized measurement site and ensure that assessments at all measurement points were taken from the same external site. No pressure was applied on the skin during scans, which were saved and analyzed off-line with publicly available imaging software (ImageJ 1.43b; NIH, Bethesda, MD, USA). These procedures are commonly used for this purpose (e.g., (9,13,28)) and involve direct measurement of MT, fascicle pennation angle (θ), and fascicle lengths (Lf) on ultrasound images. The images were collected and digitally analyzed by the same trained operator. Muscle thickness, defined as the perpendicular distance between the superficial and deep aponeurosis (17), was measured in the proximal, mid, and distal regions in each ultrasound image, and the average of the 3 values was used for further analyses. Pennation angle was measured as the angle of insertion of the muscle fascicles into the deep aponeurosis (14,25). Fascicle length was defined as the length of the fascicular path between the deep and superficial aponeurosis (Figure 1) (14,25). The VL fascicles were generally longer than the width of the probe and therefore not entirely visible in the ultrasound images. As previously described (9), the visible portion of Lf was measured accounting for fascicle curvature and the remaining part was estimated by linear extrapolation. This approach assumes linearity of fascicles and aponeuroses in the nonvisible regions and may slightly underestimate the true Lf (24). The same operator who acquired the ultrasound images performed all measurements and averaged the data collected from the 3 images at each time point. To calculate the intraobserver variation, the operator measured muscle architecture bilaterally on a single subject, repeating the measurements 20 times over 2 weeks (6). The subject was a normal control and had no change in exercise routine over the 2-week period to avoid any time-related effect or bias. The coefficient of variation (CV) was 0.8% (FL) and 2.6% (RL) for MT, 5.8% (FL) and 3.0% (RL) for θ, and 3.6% (FL) and 2.9% (RL) for Lf.
Alpine Snowboarding Simulated Race
All ALP athletes performed a standardized 15-minute warm-up that consisted of technical drills and stretching and 2 warm-up runs on a ski slope, followed by 2 inspection-runs of the course. Then, the athletes performed 10 runs with 25 gates, whose duration was approximately 35 seconds (33). The course setting followed the official international snowboard competition rules (available athttp://www.fis-ski.com/mm/Document/documentlibrary/Snowboard), with a vertical drop of ∼100 m, a horizontal distance between each gate (turning pole to turning pole) of ∼12 m, a length on the ground of ∼300 m, and a slope of ∼30% (∼16.7°). Total times were recorded to the nearest 0.01 seconds using a photocell system (Kit Racetime2 SF; Microgate, Bolzano, Italy) and the mean time of the runs was used for further analysis. The simulated race was performed on a clear day with icy snow and the temperature ranging between −2 and 5° C. The starting order was the same as for the ultrasound measurements. The resting period between runs was similar to an official race and approximately 10 minutes (the time required for the chair-lift to take the athletes to the start).
Data are presented as mean ± SD. Each variable was examined with the Kolmogorov-Smirnov normality test. The Mann-Whitney U test was used to determine whether MT, θ, and/or Lf values were different between the FL and RL. Analysis of covariance for repeated measures was performed to determine the possible differences between the changes in muscle architecture indices, with the PRE values used as a covariate. When a significant F-value was found, Bonferroni's post hoc test was applied. Statistical analyses were performed using IBM SPSS Statistics (version 20.0.0; IBM Corporation, Somers, NY, USA), and the significance level was set at P ≤ 0.05. In addition, data were assessed for practical significance using a magnitude-based inference approach (19,20) on a modified statistical spreadsheet (18). This spreadsheet calculates the standardized differences or effect sizes (ESs, 90% CI) using the pooled data PRE SDs (8). Threshold values for ES statistics were: ≤0.2, trivial; >0.2, small; >0.6, moderate; >1.2, large; and 2.0, very large (20). For within- and between-FL comparisons, the chances that the (true) changes in architecture were greater than the smallest practically important effect, or the smallest worthwhile change (0.2 × the between-subject SD), unclear or smaller than these for the RL were calculated. Quantitative chances of higher or smaller training effects were assessed qualitatively as follows: <1%, almost certainly not; 1–5%, very unlikely; 5–25%, unlikely; 25–75%, possible; 75–95%, likely; 95–99%, very likely; and >99%, almost certain. If the chance of higher or lower differences was >5%, the true difference was assessed as unclear. Otherwise, we interpreted that change as the observed chance (20).
The ALP performance time was 36.81 ± 2.06 seconds. Table 1 summarizes the PRE and POST ALP race values of 1both the FL and RL. At PRE, the RL showed a lower θ (P = 0.04, differences rated as moderate) and a higher Lf (P = 0.04, differences rated as moderate) compared with the FL; whereas the FL and RL presented similar MT values (P = 0.63, differences rated as trivial) (Table 1).
Analysis of PRE and POST the simulated race did not result in any significant differences among the muscle architecture indices (P > 0.05). Furthermore, MT (within-group change ±90% CI: −5.1 ± 8.4% of PRE value; chances that the true difference was higher/trivial/lower, 0/82/17%), θ (−4.1 ± 4.7%; 0/97/3%), and Lf (0.5 ± 7.5%; 3/96/2%) showed no meaningful changes for the FL. Similarly, MT (2.8 ± 5.9%; 3/97/0%), θ (−0.7 ± 8.6%; 3/93/4%), and Lf (−1.2 ± 5.4%; 0/98/1%) showed no meaningful changes for the RL.
The purpose of this study was to investigate acute changes in muscle architecture after an ALP simulated race and to document possible differences in the VL architecture characteristics between the FL and RL in elite ALP athletes. Our findings show no meaningful change in the intramuscular architecture of the VL after the simulated competition. In addition, θ and Lf were found to be lower and higher in the RL than the FL, respectively, at PRE, suggesting an asymmetry in the parameters of muscle architecture between the 2 legs.
To the best of our knowledge, only 3 studies have previously reported acute adaptations in quadricep muscle architecture after dynamic exercises (6,9,22). Results showed that muscle architecture is negatively affected by previously performed bouts of exercise, both during an incremental cycle ergometer test to exhaustion (6), an exhaustive leg press exercise (9), and knee extension tasks with 4 different contraction modes (22). Conversely, our findings reported no meaningful change in the VL architecture of the FL and RL. Repeated muscle contractions, both in terms of muscle action mode, force production level, and duration of action may affect the muscle architecture (16). Therefore, possible reasons for the discrepant results are that the ALP simulated race stimulus may not have been sufficiently strong to promote significant and/or consistent architectural changes in elite ALP athletes. This observation may suggest that acute muscle damage and inflammatory reactions processes that may directly influence the muscle architecture (6,9,22) could not be observable after an ALP simulated race. Possible explanations are the low work-to-rest ratio the athletes experience during the race and/or the nonexhaustive nature of the race. More details could be obtained comparing different race modalities (in terms of course characteristics and durations) and different athletes' training status.
Interestingly, at rest, θ tended to be lower by 14.0% and the Lf higher by 13.6% in the RL than in the FL. This result corroborates a previous finding that documented a muscle strength asymmetry in elite ALP snowboarders, with the RL that was ∼10% stronger than the FL (34). This is likely due to the intrinsic characteristics of ALP, given that the imposed asymmetrical position on the board leads to a heavier weight distribution on the RL during snowboarding both to turn easily and have a good board control. Therefore, this asymmetrical distribution of the center of mass could reflect a greater adaptation of the muscle characteristics in the RL. Furthermore, ALP, as skiing, is a sport in which strength is a dominant factor and eccentric contractions play an important role (33). Previous studies suggest that an increase in Lf occurs in response to eccentric exercises (13,28). Therefore, a higher eccentric stimulus on the RL, as a natural consequence of the ALP technique, may have induced a greater stretch on the muscle fibers, thereby leading to the addition of sarcomeres in series (28). Furthermore, the increase in Lf is closely associated with the lowering in θ (35). Therefore, θ could affect the force generated for a given anatomical cross-section of the VL (30) and a low degree of θ may result in an active force over wider excursion ranges and attain larger velocities of shortening (32) as well as being advantageous for reducing the loss of force transmission to the tendon (29). Therefore, both the ALP technical features and muscle loading could be responsible for the observed differences in muscle architecture between the RL and FL, thereby leading to a higher level of strength in the RL as previously observed (34).
This study has some limitations. The possible variation in ultrasound probe tilt or differences in the orientation of fascicles relative to the skin between measurements obtained PRE and POST might have introduced bias (2). However, the validity of this ultrasound technique for measurements of human muscle architecture is accepted (7), and to reduce the bias, all measurements were performed by the same operator with good levels of intraobserver reliability relative to the muscle architecture parameters (CV between 0.8 and 5.8%). Furthermore, although in principle it could be argued that limiting the ultrasound scans to a single muscle site may not be representative of other changes occurring in other muscles, this site was chosen since (i) VL activation is higher than (e.g.,) the rectus femoris of the quadricep muscle (12) and because (ii) the VL is considered the best representative of the whole quadriceps. In this regard, the VL presents a more uniform architecture throughout its length than other heads of the quadriceps (5,26). Therefore, it is the muscle that showed less inhomogeneous changes between cross-sectional area and architecture throughout the quadriceps (11,13).
An ALP simulated race seems not to be a meaningful stimulus to induce morphological changes in the VL architecture, likely because of a high recovery time between the runs that may have mitigated the acute inflammatory responses and/or the nonexhaustive nature of the race itself. Strength and conditioning coaches dealing with ALP snowboarders may consider this finding with respect to the recovery strategies between training sessions and/or different races.
Furthermore, elite ALP snowboarders presented morphological asymmetries between the FL and the RL, confirming previous observation (34). This might predispose the athlete to musculoskeletal injuries and could have a practical relevance in (i) quantifying the functional deficit consequent to injury and (ii) exercise prescription.
The authors thank the athletes for their efforts and cooperation. The authors also extend our gratitude to the coaches (Erich Pramsohler, Luca Migliorini, Diego Montalbano, and Matteo Pirletti) for their valuable technical support during data acquisition, Matteo Fumagalli and Esaote Biomedica for the collaboration, and to the Italian Winter Sports Federation for support.
No support was provided for this study by any manufacturer of the instruments used. No conflicts of interest, financial or otherwise, are declared by the authors.
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