Data are presented as mean ± SD. Mean and standard deviation (SD) were calculated for all variables. Statistical analysis was performed using SPSS 25.0 for Windows (SPSS Inc, Chicago, IL, USA). Variables were analyzed by a 2-way analysis of variance (ANOVA) with repeated measurements: group (EG and CG) and time (pre- and post-training).
Follow-up comparisons were made with paired t-tests within each group. Statistical significance was set at p ≤ 0.05.
4 RESULTS
The key performance data are shown TABLE 2. No substantial improvements were found in the CMJ in any group compared with the pretest but EG showed substantial improvements in CMJ +20kg and CMJ +40kg and CG in CMJ +20kg, despite no overall interaction effect in the 2-way ANOVA. The 200 meters running test results within-group analysis revealed substantial changes from pre- to post-training for most of the total and split times.
Results from the between-groups analysis are illustrated in Figure 4 and Figure 11. No significant group by time interaction was found in any jump test. Furthermore, no significant group by time interaction was observed for any of the 200 meters running test, total or split times.
TABLE 2. Outcome variables before (PRE) and after (POST) 8 weeks of resistance training in the flywheel (EG) and control (CG) group, Mean ± SD
EG CG
4.1 Jumps
Both protocols showed comparable increases in CMJ, CMJ +20kg and CMJ +40kg height (Figure 4). No significant group by time interaction or within-group differences were observed for the CMJ test (p=0.863). Within-group differences for the CMJ were in the EG 5.7 ± 6.9%; p = 0.057, and in the CG group 4.8 ± 12.2%; p = 0.265 (Figure 5).
Figure 4. CMJ jump tests group mean differences
Figure 5. Pre- and Post-training CMJ height and mean change. No significant group by time interaction (p > 0.05). No significant planned comparisons within-group differences (p > 0.05).
No significant group by time interaction was observed for the CMJ +20kg test (p=0.474).
Significant within-group differences for the CMJ +20kg were observed in the EG (7.3 ± 7.4 %; p = 0.027) and CG group (11.1 ± 12.9 %; p = 0.032). Figure 6 shows the CMJ+20 kg height (cm) results before and after the intervention.
Figure 6. Pre- and Post-training CMJ + 20 kg height and mean change. No significant group by time interaction (p > 0.05). Significant planned comparisons within-group differences (p < 0.05).
There was no significant group by time interaction in CMJ+40kg test (p=0.625).
Significant within-group differences for the CMJ were observed in the EG (6.1 ± 3.1%;
p = 0.002) vs. CG group (9.2 ± 16.1%; p = 0.134). Figure 7 shows the CMJ+40 kg height (cm) results before and after the intervention.
Figure 7. Pre- and Post-training CMJ + 20 kg height and mean change. No significant group by time interaction (p > 0.05). Significant planned comparisons within-group differences in EXP group (p < 0.01).
4.2 Runs
No significant group by time interaction was observed for any of the 200 meters running test total or split times. However, planned comparisons within-group analysis revealed statistically significant changes from pre- to post-training for most of the total and split times.
There was no significant group by time interaction in 20 meters sprint time (p=0.517).
Planned comparisons of the 20 m sprint test revealed significant within-group changes in both groups (EG: -3.2 ± 1.7%, p = 0.001 vs. CG: - 2.6 ± 2.2%, p = 0.008). Figure 8 shows the 20 m sprint times before and after the intervention and mean change.
Figure 8. Pre- and Post-training 20 meters sprint time and mean change. No significant group by time interaction (p > 0.05). Significant planned comparisons within-group differences in CG (p <
0.05). Significant planned comparisons within-group differences in EG (p < 0.01).
There was no significant group by time interaction in 40 meters sprint time (p=0.605).
Significant within-group differences were observed in the EG (-3.0 ± 1.3%; p < 0.001) and CG group (-2.6 ± 1.9%; p = 0.003). Figure 9 shows the 40 meters sprint time (s) results before and after the intervention and mean change.
Figure 9. Pre- and Post-training 40 meters sprint time and mean change. No significant group by time interaction (p > 0.05). Significant planned comparisons within-group differences in both groups (p < 0.01).
There was no significant group by time interaction in 200 meters total sprint time (p=0.572). Significant within-group differences were observed in the EG (-1.8 ± 1.6%; p
= 0.013) and CG group (-1.5 ± 1.0%; p = 0.002). Figure 10 shows results before and after the intervention and mean change.
Figure 10. Pre- and Post-training 200 meters sprint time and mean change. No significant group by time interaction (p > 0.05). Significant planned comparisons within-group differences in EG (p < 0.05). Significant planned comparisons within-group differences CG (p < 0.01).
The fatigue profile was similar between the groups. Furthermore, speed and COD profile i.e. first two shuttles improvements, were similar between the groups without any significant group by time interaction. Similar findings were found in speed endurance profile. In summary, even though EG improved 14/19 of the running test total or split times results more than CG, there were no group x time interactions (Figure 11).
Figure 11. Running test group mean differences
4.3 Power output
In the maximal power output test for the EG, there were significant within-group differences on 5RM (33 ± 23 %; p = 0.012) and peak repetition (31 ± 25 %; p = 0.018) AVG power development (W). Figure 12. shows the results before and after the intervention.
Figure 12. Pre- and Post-training power output (W) 5 repetition and 1 repetition peak average power and mean change. Significant planned comparisons within-group differences (p < 0.05).
5 DISCUSSION
This study aimed to assess the effects of 8 weeks of FW training compared to traditional strength training on neuromuscular performance of elite ice-hockey players. The results showed that both training interventions led to performance improvements of similar magnitude. There were no significant group x time interactions, but several main training effects.
The current study shows that FW training is an effective method for improving several aspects of strength and power with relevance for ice-hockey performance. Indeed, there were substantial improvements in capacities highly related to athletic performance, such as vertical jump height, running speed and endurance as well as power output. These findings are supported by previous meta-analyses (Petre et al. 2018, Maroto-Izquierdo et al. 2017a) where several aspects of neuromuscular performance have been shown to be enhanced by FW training. Thus, elite ice-hockey players could include flywheel training into their training regimen for performance enhancement.
The current study showed that FW training induces significant improvements in power (33%) after 14 sessions. This was an important finding given that muscle strength, power and anaerobic capacity are key physiological characteristics for hockey players on the ice (Roczniok et al. 2016). The magnitude of improvement was in line with Petre et al.
(2018), who reported a significant increase of 25% in power of large effect size from pre- to post-test after 4-24 weeks of flywheel training and 1-3 sessions per week. Similarly, Maroto-Izquierdo et al. (2017a) reported that muscle power is the training outcome that experienced the greatest increase after a period of FW training with eccentric overload in healthy subjects and athletes.
In this study, there were significant improvements (around 3%) in 20 and 40 meters sprint time in both groups. In the 200 meters sprint, the improvement was 1.5%. Comparable results were found by Petre et al. (2018) who found significant improvement of 2.4% in horizontal displacement with a large effect size from pre- to post-test after 6–10 weeks of flywheel training 1–3 times per week. For vertical displacement, the current study report performance improvements of 5-7% in CMJ jumps. Similar findings were found by Petre
et al. (2018) who showed that there was a significant increase of 6.8% in vertical displacement with a large effect size from pre- to post-test.
This study showed similar magnitudes of improvements of performance in both training groups. This might be due the small sample size and the fact that the training was programmed in a similar manner in both groups and was based on strength training methods already proven effective. Furthermore, since all the players were trained athletes with background of several years strength training, small improvements are expected.
It is evident that strength training with free weights is an efficient way to gain performance enhancement for elite athletes. This study supports that conclusion. Well programmed general strength training interventions are effective and experienced younger athletes tend to develop significant improvements in performance in a short period of time. Most of the earlier studies have compared FW training to conventional strength training in one single exercise to other single exercises like FW leg press exercise vs. weight-stack leg press exercise but not the multi-movement exercise program as in this study (Maroto-Izquierdo et al. 2017b). Núñez Sanchez & Sáez de Villarreal (2017) earlier reported that the ability to produce an eccentric overload in the FW system appears to require some earlier experience of the training method. The ability to produce an eccentric overload is indicative of greater mechanical loading, potentially resulting in more robust training stimulus. None of the players in this study had earlier experience of FW training which can influence of the capacity to achieve eccentric overload during the exercise. Thus, it is possible that performance could have been even better if the players had earlier experience of the training method. In contrast, the players were experienced to training with free weights, which can potentially favor improvements in the control group. Ideally, future studies should compare FW training to other conventional strength training methods with experienced users to the training method per se.
In the research literature, there is some evidence that FW and eccentric overload training is superior to conventional strength training in terms of performance enhancement as well as muscle anabolic response and adaptations in well-trained athletes (Friedmann-Bette et al. 2010, Norrbrand et al. 2011, Maroto-Izquierdo et al. 2017b). This study did not support that. Well-trained athletes familiar to free weights but not to FW might benefit more from free weights. Conversely, more experienced athletes using eccentric overload training
could perhaps reach better performance gains and muscle adaptations as shown by Friedmann-Bette et al. (2010).
One of the goals of this study was to load all the main leg muscles used in ice-hockey with large forces. As Kaartinen (2019) presented, hockey players would gain from training programs involving motions of large forces and with maximal range of motion as extension of the knee joint at the beginning of the recovery phase predicted better skating performance. Unilateral squat with FW machine mimics this propulsion action.
On the other hand, unilateral training with FW squat machine mimics COD, skating thrust mechanics and SSC stimulus on-ice and leaves opportunity to use the medio-lateral arm swing to increase GRF’s on the outer leg which is almost impossible with barbell training.
These are all important and relevant aspects when designing general and sports specific strength training exercises to mimic the demands of ice-hockey. Deep squats, full-range knee extensions, and full-range leg presses are exercises that need to be incorporated into a hockey training program, since these exercises mobilize the lower extremities through a range of motion similar to that for hockey skating (Lafontaine 2007). Behm et al. (2005) presented that either skating-specific resistance exercises or exercises that can specifically isolate the hamstrings are required to provide the necessary level of activation for hockey skating. In that regard, the FW leg curl is a viable option and is complemented by the FW squat since it increases the hamstrings-to-quadriceps ratio alone but not with the traditional squat training using barbell. In addition, the specific FW squat training alone increases hamstring ECC & quadriceps CON ratio which could be beneficial for injury prevention (Coratella et al. 2019).
Running force is generally generated and applied to the ground in a single sagittal plane.
Skating force, however, is applied to the ice not only sagittally but also through the frontal plane. This difference in the application of force requires differences in joint mechanics, particularly in the hip. Therefore, testing and evaluating linear skating speed should also ideally be done on-ice. Off-ice testing measures that will accurately measure progress are necessary to determine the effectiveness of prescribed training regimens, especially during the off season. These tests should be relatively easy to administer yet highly correlated with skating speed and hockey performance (Runner et al. 2015). During the off-season, the availability of ice time is reduced, and thus, for adequate monitoring of off-season training, testing would be appropriate to take place off-ice also. Farlinger et
al. (2007) presented that measures of horizontal power are the strongest predictors of on-ice skating performance that includes an acceleration component typical of normal game play. Mascaro et al. (1992) reported that vertical jump anaerobic power was the single best predictor of skating speed per se. Behm et al. (2005) found significant correlations between skating performance and the sprint and balance tests but not in CON squat, jump, drop jump, 1 repetition maximum leg press or flexibility tests. The off-ice tests used in this thesis were pre-determined by the ice-hockey team and Varala Sports Institute.
FW training is a safe form of exercise to achieve short bouts of eccentric overload controlled by the user and the current study confirmed that there is no need for prior experience to reach some benefit from FW training. There are also several methodological options to manipulate the ECC load when players can tolerate more ECC force and get customized with the traditional FW training resistance paradigm. ECC training has also been shown to be efficient to prevent lower limb muscle injuries and muscle problems in elite athletes (Goode et al. 2015, Harøy et al. 2018). Therefore, high priority should be placed on hockey players lower limb muscles for injury prevention. Douglas et al. (2016) have determined that ECC training is also a potent stimulus for enhancements in muscle mechanical function, and muscle-tendon unit morphological and architectural adaptations associated with a faster (i.e. explosive) phenotype.
Free weights, FW machines and other resistance training modalities have and will have their own role and benefits for athletic development. Thus, coaches and athletes should consider implementing a variety of different training methods to enhance athletic performance.
A limitation of this study was the non-randomization of the players which may have influenced on the player characteristics even though players characteristics were comparable across groups. Also, the strength training sessions were controlled by the players themselves by completing an exercise diary which could possibility give rise to errors compared to supervised training. Furthermore, it would be of interest to analyze the effect of this intervention on the most representative performance tests in ice-hockey on-ice. As earlier training studies have shown, it is difficult to get significant group x time interactions across training interventions in small sample sized studies where the improvements are not expected to be large. Further studies are needed to analyze the
effects of eccentric overload FW training on indices of ice-hockey performance on-ice and compare them to well-designed conventional strength-training programs. This could be done both for reduction of injuries and for improving performance on-ice, in larger sample sized interventions with players experienced in the training method.
6 CONCLUSION
Based on the findings of this experimental training study, it is concluded that both flywheel and conventional resistance training improves performance proxies relevant to ice-hockey players. There were no significant group x time interactions, suggesting similar magnitudes of improvements across groups. Thus, FW training seems to be an effective training method to improve neuromuscular performance in elite ice-hockey players. However, flywheel training does not elicit superior improvements in performance compared with traditional strength training in players with no experience of this training method.
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