Strength, Velocity And Power In Jump Squat Using Light And Medium Load In Junior Speed Skaters

The optimal load for highest power output

Heavy resistance training uses a relatively heavy load (>80% of 1RM) and is performed with a relatively slow velocity because of a large external resistance that must be overcome (Hakkinen & Komi, 1985; Harris, Stone, O'Bryant, Proulx, & Johnson, 2000; Hoffman, Ratamess, Kang, Rashti, & Faigenbaum, 2009). This method has been reported to increase maximum muscular strength and to result in enhanced muscular power or dynamic performance (Adams, O'Shea, O'Shea, & Climstein, 1992; Duchateau & Hainaut, 1984; Thompson et al., 2010) or to maintain training speed specificity and maximize mechanical power output.

Some authors have investigated the use of unloaded and loaded squat jumps in their assessment of lower body power while collecting force plate data (Baker et al., 2001; Sands et al., 2005; Stone et al., 2003; Wilson, Newton, Murphy, & Humphries, 1993). It has been suggested that when training to increase muscular power using loads which emphasizes the athlete’s maximum power output may be advantageous for maximizing improvements in performance (Baker & Newton, 2005; Cronin, McNair, & Marshall, 2001; Kilduff et al., 2007; McBride, Triplett-McBride, Davie, & Newton, 2010). However, in his study Knudson (2009) is saying that, the peak power is not a fixed characteristic of a certain athlete, having fluctuations depending on different factors.

Programs dedicated to the development of power, however, may require athletes to train with loads substantially lower than the 1RM (Bevan et al., 2010; Fleck & Kraemer, 2004; Thomas et al., 2007; Wilson, Newton, Murphy, & Humphries, 1993; Zatsiorsky & Kraemer, 2006) as the value mentioned previously, respectively (> 80% from 1RM). One of the primary points of contention on the development of power through resistance exercise has been the type of loading to be used. Furthermore, because peak power occurs between 30 and 50% 1RM (Thomas et al., 2007), testing programs should evaluate low-speed strength with maximal loads, and the ability to perform high-velocity movements with submaximal loads.

Validity of the instruments assessing the power output

Over the past 5 years, many studies have examined peak power output during training using either a Tendo FiTROdyne or a Tendo Weightlifting Analyzer (TENDO Sports Machines; Trencin, Slovak Republic) (Baker & Newton, 2005; Hoffman et al., 2009; Jones, Fry, Weiss, Kinzey, & Moore, 2008; Rhea, Peterson, Lunt, & Ayllo´n, 2008). In the studies that have utilized the Tendo Weightlifting Analyzer as a mean to measure power output it has been shown that results are reliable to asses power, force and velocity.

Thompson et al. (2010) in their study used the Tendo as an indicator for the peak power during a bench press. These measurements were then analysed through ratio and allometric scaling to determine its influence on normalizing peak power.

Overall, the Tendo has been used mainly for the comparison of different trials to each other, which has confirmed the reliability of the Tendo. By validating the Tendo, data collected are not only reliable but the measurements are correct in relationship to what is being measured. For example, Thompson et al. (2010) recently used peak power values from the Tendo Weightlifting Analyzer to normalize differences between division I collegiate football linemen and non–linemen using ratio and allometric scaling procedures.

There were no significant differences between or within the groups for any of the participant characteristics variables pre or post intervention (Table 1 ).

1RM Testing

Before each test period, the subjects had the opportunity to familiarize themselves with the procedures applied (with 48h before). The day of familiarization assumed the same steps in the test protocol. Before the start of the test was performed a 10-minute warm-up on the ergometric bike (XTPRO Bike 600, Tehnogym Usa Corp., U.S. A), followed by 5 minutes stretching exercises. After approx. 2 minutes the subjects started 1RM test protocol (Murray, 2005). This protocol consists of a warm-up with an estimated load of 10 reps x 50%-, 5 reps x 70%, 3 reps x 80% and 1 rep x 90% of 1RM (3 minutes rest between sets). After warm-up the load was progressively increased, each subject having 3-4 attempts (maximum efforts) to determine 1RM.

After the determination of 1RM, subjects performed a squat jump using the Olympic bar (20kg) with the additional load according to the test protocol, 30% and 55% of 1RM. To measure the desired variables, the Tendo Weightlifting Analyzer (TENDO Sports Machines, Trecin, Slovak Republic) was used and the mat (Tendo WL package) to measure the jump height. The data was collected using the software Tendo Softaware Computer V-5 (Version 6.0.1, Slovak Republic).

Before testing, a series of 6 repetitions were performed only with the bar. The load used was increased exponentially starting from 30% to 55% of 1RM. Subjects were told that after reaching this point to accelerate the concentric phase of movement as quickly as possible, followed by a vertical jump with maximum height. 3 attempts were allowed for each load.

Squat jump testing

The study has a longitudinal design, in which three groups participated, the two experimental groups and one control group (C) (Table 1 ). Two treatment groups followed two different training protocols, respectively SJ (30%) (n = 5): training with 30% of 1RM) and SJ (55%) (n = 5:) training with 55% of 1RM) after which they performed a squat jump test with both loads 30% and 55% of 1RM. The third group served as controls (C). The test periods were grouped in two weeks, pre and post-test and the intervention period of 8 weeks of strength training (2 times a week with a duration of approx. 60min). All training was assisted by the researcher.

Testing involved a light-weight squat jump with 30% of 1RM and medium -weight squat jump with 55% of 1RM. Before each test the subjects performed a warm-up on the ergometric bike for 10 min with a standard resistance imposed - 105W (XTPRO Bike 600, Tehnogym Usa Corp., U.S.A), followed by 5 minutes stretching exercises. Approximately 2 minutes later testing began. All trainings were performed using an Olympic bar (Olympic Sportmann Romania, 20kg) to which the load was added according to 1RM determined on each subject. To evaluate the peak power (PP), peak force (PF), peak velocity (PV) and jump height (JH) for each repetition we used Tendo Weightlifting Analyzer (TENDO Sports Machines, Trecin, Slovak Republic) and in addition was used the mat to measure the height of the jump. Data was collected using the software (Tendo Softaware Computer V-5. Version 6.0.1, Slovak Republic).

The training program included two strength trainings per week for the experiment group. The subjects in the experiment group performed a warm-up of 10 minutes on the ergometric bike with a standard resistance - 105W (XTPRO Bike 600, Tehnogym Usa Corp., U.S. A), followed by 5 minutes stretching exercises. Approximately 2 minutes later testing began. Both experimental groups performed two series of 6 repetitions with 20kg, after which they followed two different types of training protocols according to the sampling of those with light load 30% of 1RM, a series of 5 sets and with medium load 55% of 1RM, a series of 4 sets.

The number of repetitions performed in each set was determined on the basis of the decrease of the peak power output of 15%. This level was chosen as a reference point corresponding to a significant decrease in the maximum speed obtained between the required loads (30%, 55%) each repetition was considered correct when the angle determined by the knee flexion was 90 degrees, representative for speed skating, ideal for producing maximum force and power in a side push, followed by an explosive jump to achieve maximum jump height. The task of each subject was to perform each repetition at maximum speed, exerting a maximum force. The control group did not perform additional explosive exercises and were told to follow their daily training regimen between the test periods.

Squat jump testing comparisons between variables

After a 8-week strength training period, notable changes were observed by the testing protocol. We found a significant increase in jump height (JH) for (C) group with 30% of 1RM and for the SJ (30) and SJ (55) for both loads tested. Concerning the peak power (PP), results showed a significant increase for (C) group measured with 30% of 1RM for SJ (30) with 55% and for the SJ (55) for all loads tested. For the peak velocity (PV), results showed a significant increase for (C) group with 55% of 1RM, for SJ (30) with both loads used and for the SJ (55) with 30% of 1RM and a very significant one with 55%. Results obtained for the peak force (PF), showed for (C) group a significant increase with 30% for SJ (30) and SJ (55) with both loads tested.

Squat jump testing correlations between variables

A Colton correlation was computed to assess the relationship between the variables measured peak power, peak force, peak velocity and jump height for control and intervention groups. The analysis revealed that there is a positive and strong correlation between all variables. These results support the hypothesis that a 8-week strength intervention in speed skaters would result in significant changes in peak power, peak velocity, peak force and height jump during a squat jump. Our findings for the three groups are described below:

The correlation between variables measured in (C) group showed Post intervention for the 30% of 1RM tested, a very good correlation between all variables HJ- PP (r/ρ = 0.84, p <0.001), HJ- PV (r/ρ = 0.87, p < 0.001) and HJ- PF (r/ρ = 0.81, p < 0.001) and PV- PP- (r/ρ = 0.89, p < 0.001) ; PV-PF (r/ρ = 0.82, p 0.001) same values were found for 55% of 1RM post intervention.

The correlation between variables measured in SJ (30) group showed Post intervention with 30% of 1RM tested, a good and positive correlation between HJ-PP ((r/ρ = 0.70, p 0.001), HJ-PF ((r/ρ = 0.63, p 0.001); PP-PV (r/ρ = 0.70, p 0.001), and for the 55% of 1RM a very good correlation and positive between HJ-PP (r/ρ = 0.98, p 0.001), HJ-PV (r/ρ = 0.98, p 0.001), PP-PV (r/ρ = 0.98, p 0.001).

The correlation between variable measured in SJ (55) group Post intervention with 30% of 1RM, was very good and positive between HJ-PP (r/ρ = 0.96, p 0.001), HJ –PV (r/ρ = 0.98, p 0.001), HJ-PF (r/ρ = 0.80, p 0.001); PP-PV (r/ρ = 0.98, p 0.001), PP-PF (r/ρ = 0.78, p 0.001), PV-PF (r/ρ = 0.81, p 0.001). And with 55% of 1RM, very good and positive between HJ-PP (r/ρ = ,0.93, p 0.001), HJ-PV (r/ρ = 0.94, p 0.001); HJ-PF (r/ρ = 0.82, p 0.001), PP-PV (r/ρ = 0.85, p 0.001), PP-PF (r/ρ = 0.93, p 0.001), PV-PF (r/ρ = 0.75, p 0.001).

• Statistical analysis for jump height obtained for the two loads confirmed between Pre and Post training intervention statistical significant differences (p < 0.001) between (C), SJ (30) and SJ (55) groups tested with 30% and 55% of 1RM.

• Statistical analysis for peak power (PP), showed between Pre and Post training intervention: significant differences for SJ (30) with 55%, for (C) and SJ (55) with both loads.

• For peak velocity (PV), were observed between Pre and Post training intervention: significant differences (p < 0.001) for (C) with 55% of 1RM, for SJ (30) with all loads and for SJ (55) only with 30% of 1RM.

We found very significant differences (p < 0,001) for SJ (55) with 55% of 1RM. For peak force (PF) were observed between Pre and Post training intervention: significant differences (p < 0.01) for (C) with 30% of 1RM, for SJ (30) SJ (55) with both loads.

Table 2 presents the results obtained for each variable in pre and post testing periods. No significant differences were observed for any strength measures between the intervention and control groups at baseline. The change in absolute maximal strength in the intervention group SJ (30%) (Pre 90.0 ± 9.8 to Post 102.5 ± 10.2), was significant different from Pre to Post- test within the group. However, the change in relative maximum strength (1RM back squat) in the intervention groups SJ (30%) and SJ (55%) (Pre 96.5 ± 10.1 to Post 112.5 ± 10.3) was significantly increased from Pre to Post test (p < 0.05).

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Training design to enhance power output

Taking into account the above mentioned we suggest the use of different types of exercises, like Olympic-style lifts and their derivatives (e.g., power clean, snatch) that are also considered the best training exercises to maximize muscular power and dynamic athletic performance because they are multi joint exercises, they do not have the problem of deceleration phase, and they produce some of the highest average human power outputs of all the resistance-training exercises (Haff et al., 2005; Stone et al., 2003). Besides that, results are indicating that both heavy resistance and explosive-type resistance training should be included in resistance-training programs to develop muscular power and athletic performance.

Maximal mechanical power has been thought to occur at a resistance of 30% of maximum isometric strength (Faulkner, Claflin, & Mccully, 1986) or 30– 45% of 1 repetition maximum (1RM) (Harris et al., 2000; Newton, Cormie, & Cardinale, 2011).This findings from the current investigation are consistent with these previous findings. Training with an optimal load and thus velocity results in velocity-specific increases in muscle activation. Thus, it appears that the velocity of the movement, as controlled by the load, plays a key role in improving high-velocity performance capabilities and power output.

As reported, combined training method has also been proven useful to develop muscular power and a wide variety of athletic performances (Adams et al., 1992; Haff et al., 2001; Rhea et al., 2008). This combination could be heavy resistance/plyometric training (Adams et al., 1992) heavy resistance/explosive-type resistance training (Harris et al., 2000; McBride et al., 2010), heavy resistance training/sports-specific task or explosive-type resistance training/sports-specific task (Cormie et al., 2011).

Training design to enhance velocity

In conjunction with sport-specific testing and 1RM testing during off – ice season assessing the force-velocity qualities of the leg extensors against a range of external loads can provide the strength and conditioning coach with insight into the training needs of an individual athlete. If a speed skater’s results demonstrate that his acceleration and velocity is poor as external load is added, then the coach can use this information by designing the training accordingly (i.e., emphasis on heavy load strength and high load power training). If another speed skater demonstrates that he decreases very little in his acceleration and velocity qualities as external load is added, yet low load power is considered an important attribute for this athlete, the coach can design training accordingly (i.e., emphasis on unloaded/low load jumps, plyometrics, etc.). However, this type of training model used in this investigation is more applicable to sports in which velocity changes over the course of a specific movement.

Results show that this type of training induces improvements in all variables measured which contributes to actual speed skating performance on and off ice. Additionally, these findings could help strength and conditioning coaches adjusting the strength program for ones weaknesses regards one of the aspects mentioned above among young skaters. Therefore, this study makes it possible to evaluate multiple variables during a squat jump with different loads and measuring if whether or not skaters are capable of maintaining physical capabilities such as force, speed and power during a period of time.