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Using Squat Testing to Predict Training Loads for Lower-Body Exercises in Elite Karate Athletes

Wong, Del P1; Tan, Erik C H2; Chaouachi, Anis3; Carling, Christopher4; Castagna, Carlo5; Bloomfield, Jonathan6; Behm, David G7

Journal of Strength and Conditioning Research: November 2010 - Volume 24 - Issue 11 - p 3075-3080
doi: 10.1519/JSC.0b013e3181d65071
Original Research
Free

Wong, DP, Tan, ECH, Chaouachi, A, Carling, C, Castagna, C, Bloomfield, J, and Behm, DG. Using squat testing to predict training loads for lower-body exercises in elite Karate athletes. J Strength Cond Res 24(11): 3075-3080, 2010-The purpose of this study was to determine the relationship between squat loads and 2 bilateral and 2 unilateral stepping lower-body exercises in predominantly unilateral movement elite athletes (Karate). Equations to predict loads for lower-body exercises based on the squat load were also determined. Fourteen male elite Karate athletes (age = 22.6 ± 1.2 years) performed 6 repetition maximum (RM) of the following free-weight bilateral exercises: back half squat, deadlift, leg press and unilateral stepping exercises, lunge; and step-up. Results showed that 6RM squat load was significantly (p < 0.001) correlated with deadlift (r = 0.86), leg press (r = 0.76), lunge (r = 0.86), and step-up (r = 0.92). Linear regression showed that the 6RM squat load was a significant predictor for deadlift, leg press, lunge, and step-up (R2 range from 0.57 to 0.85, p < 0.001). The following 6RM prediction equations were determined: (a) Deadlift = squat load (1.12)-16.60 kg, (b) Leg press = squat load (1.66) + 16.10 kg, (c) Lunge = squat load (0.61) + 9.39 kg, and (d) step-up = squat load (0.85)-10.36 kg. Coaches and fitness professionals can use the 6RM squat load as a time effective and accurate method to predict training loads for both bilateral and unilateral lower-body exercises with quadriceps as the prime mover. Load prescriptions for unilateral exercises should take into account the type of athletic population.

1Department of Health and Physical Education, The Hong Kong Institute of Education, Tai Po, Hong Kong; 2Conditioning Center, National Sports Institute of Malaysia, Malaysia; 3Tunisian Research Laboratory “Sport Performance Optimisation,” National Center of Medicine and Science in Sports, Tunis, Tunisia; 4LOSC Lille Metropole Football Club, Centre de Formation, Domain de Luchin, France; 5Faculty of Medicine and Surgery, School of Sport and Exercise Sciences, University of Rome Tor Vergata, Rome, Italy; 6Sports Institute of Northern Ireland, United Kingdom; and 7School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John's, Canada

Address correspondence to Del P. Wong, delwong@alumni.cuhk.net.

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Introduction

The squat is one of the most frequently prescribed exercises in high performance athletic training (12,13,15,32). The multiple repetitions measurement in the back half squat has been found to be highly repeatable with an intraclass correlation coefficient (ICC) of 0.95 (25) and is highly correlated with 1 repetition maximum (1RM) values (r > 0.96) (23). In addition, previous studies have found that muscular strength in the back half squat had a high association with jump (38), sprint (38), power (4), and sport performance (28) in elite athletes. To prescribe strength training programs, the determination of exercise loads can be achieved objectively by calculating a percentage from the maximal strength represented by 1RM, or subjectively by trial and error (13,15,32). The latter method can be employed but is inaccurate, varies between subjects, and does not conform to the guidelines of the National Strength and Conditioning Association (3,15,36).

The prediction of 1RM from multiple repetitions measurement offers a practical advantage over 1RM testing in that only core exercises that recruit large muscle groups and multiple joints are suggested for 1RM measurement. In contrast, exercises such as the deadlift are not recommended because the weak stabilizing muscles of the lower back would become highly fatigued after several testing sets and maintaining a correct body position throughout the test would be difficult (3). In addition, unilateral exercises such as lunges and step-ups place unequal loading on the limbs and are not recommended for the 1RM test (3). In this regard, the multiple repetition measurement has an advantage over the 1RM because the former measurement can be made on both the assistance and unilateral exercises (14,23).

Ebben et al. (14) reported high explained variance between 6RM loads of squat and other lower-body exercises (R2 ranged from 0.62 to 0.81) among collegiate athletes and recreationally active students. However, Ebben et al. (14) suggested that the prediction equations from their study could only be generalized to similar populations. Karate, for example, is a martial art that places emphasis on unilateral striking patterns. Although 1RM testing typically involves core exercises such as squat, bench press, cleans, and other large muscle group bilateral activities, it is not known if the regression equations and correlations derived from Ebben's study for collegiate and recreationally active individuals could specifically apply to elite athletes in whom unilateral actions are emphasized. Furthermore, Ebben's results showed that the lowest correlations occurred between squats and unilateral actions such as lunges (R2 = 0.62), step-ups (R2 = 0.71), and single-leg knee extensions (R2 = 0.67). The greatest correlation occurred between the bilateral squat test and the bilateral deadlift test (R2 = 0.81). Hence, Karate athletes with their unilateral striking emphasis may require substantially different correlation and regression equations between the 6RM bilateral squat and unilateral actions such as the lunge and step-up.

Stability is a mitigating factor in the production of force during a resisted action. A number of studies report decreased force output in less stable conditions (5,6,10,21,22,26). Lunges and step-ups are performed with unilateral stepping actions reducing the area of support and decreasing stability as compared with bilateral actions such as squats, leg presses and deadlifts with wider support bases. Behm et al. (8) reported a significant correlation between the maximum skating speed and static balance scores in young ice hockey players. Athletes who participate in team sports that emphasize stability such as ice hockey or in individual sports such as Karate that require great stability when kicking, striking or evading a blow may express a different relationship between more stable resistance activities such as 6RM squats and leg presses as compared with more unstable resisted activities such as lunges and step-ups.

The unique nature of Karate athletes who use unilateral striking actions under relatively unstable conditions suggests that previous prediction equations that were based upon individuals using predominately stable bilateral actions may not be appropriate for this type of population. Therefore, the purpose of this study was to determine the relationship between 6RM loads of bilateral and unilateral exercises such as the bilateral squat, deadlift, and leg press vs. the unilateral stepping actions of lunges and step-ups in a group of elite athletes (Karate) in whom the emphasis is placed on stability and unilateral actions. It was hypothesized that significant correlations exist between the bilateral squat and the unilateral stepping actions of the lunge and the step-up and that these correlations would exceed the reported correlations of collegiate and recreationally active individuals (11). This study also aimed to create prediction equations, based on the squat load, to determine the loads for lower-body exercises in these types of athletes (elite athletes with a unilateral striking emphasis).

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Methods

Experimental Approach to the Problem

To test the hypothesis that a correlation exists between the 6RM of squat and other bilateral and unilateral low-body exercises, tests of deadlift, inclined leg press (bilateral), lunge and step-up (unilateral stepping actions) capacity were undertaken. Athletes performed 5 exercises in 3 visits separated by a 48-hour period. The exercise order during the testing day was counterbalanced to limit exercise order effect on performance (35). All athletes were instructed not to participate in resistance training 48 hours before testing. The present exercises were selected because these are frequently used in resistance training performed by high-performance elite athletes (12,13,15,32) and could be quantified by external loads (14). The 6RM was chosen to compare findings with those reported in a previous study (14). Furthermore, assistance type and unilateral exercises such as lunge and step-up are not commonly tested for 1RM because the high external loading can place athletes at risk of injury (3). These exercises were included in this study because one of the objectives was to investigate if correlations between squats and unilateral type exercises were high in unilateral predominant athletes. The 6RM squat load was the predictor variable of the other 4 exercises.

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Subjects

Fourteen male elite Karate athletes participated in the study during the precompetition preparation phase. All of these were national senior athletes from Malaysia, and 3 were world championship medalists. Their age, body mass, height, and body mass index are reported in Table 1. All athletes were properly informed of the experimental risks and benefits of this study and signed an informed consent document before the investigation. The study was conducted according to the Declaration of Helsinki, and the study was fully approved by the Clinical Research Ethics Committee.

Table 1

Table 1

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Measurements

Before any exercise in the first visit to the sport science laboratory, skinfold thickness was measured with a Harpenden skinfold caliper (British Indicators Ltd., United Kingdom) at 7 sites (biceps, triceps, subscapular, supraspinale, abdomen, front thigh, and medial calf) following the protocol recommended by International Society for Advancement of Kinanthopometry (24). Skinfolds in all athletes were taken by the same nutritionist trained in anthropometric measurements. Body density was determined according to the equation of Withers et al. (39), whereas the percentage body fat was calculated from body density using Siri's equation (33) (Table 1).

All athletes performed a 10-minute warm-up including dynamic and static stretching. After the warm-up, athletes performed one warm-up set of 6 repetitions at ∼65 to 75% of their perceived maximal load of each exercise. Athletes were familiar with the exercise technique because they regularly trained using these movements. Loads were assessed by having the athletes perform the 6RM tests for the back half squat, bent-knee deadlift, lunge, step-up on a box (0.37 or 0.40 m height depending on the athletes), and 45° inclined leg press (Figure 1). The techniques and guidelines of these exercises were described by the second author in this study and followed the instructions of National Strength and Conditioning Association (11). Athletes performed each exercise at their volitional velocity that was approximately 2 seconds in both concentric and eccentric phases. All athletes attained at least 6 repetitions of the 6RM loads, and 4 min of recovery was allowed between exercises (14). Strong verbal encouragement was given to each athlete during all test sessions. The second author in this study, who is a Certified Strength and Conditioning Specialist, monitored all test sessions to ensure proper exercise technique and safety. Exercise testing was performed over 3 days with 48 hours of recovery between testing. The exercise order during the testing day was counterbalanced to limit exercise order effect on performance (35).

Figure 1

Figure 1

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Statistical Analyses

Values are presented as mean ± SEM. Pearson's product moment correlation coefficient was used to examine the relationship between squat and the other 4 exercises. Linear regression analysis was used to develop the prediction equations for each of the 4 exercises with squat load being a predictor. The prediction equations for each of the exercises were crossvalidated using the predicted residual sum of squares (PRESS) statistic, as previously recommended and described in the literature (18). The significant level was defined as p ≤ 0.05. Ten athletes were instructed to perform the reliability test 7 days after the initial tests. Intraclass correlation coefficient across tests showed that the 6RM tests were highly repeatable (ICC > 0.95).

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Results

The 6RM loads for the squat, deadlift, leg press, lunge, and step-up are given in Table 1. Results showed that 6RM squat load was significantly correlated with the 4 lower-body exercises: deadlift (r = 0.86, p < 0.001), leg press (r = 0.76, p < 0.001), lunge (r = 0.86, p < 0.001), and step-up (r = 0.92, p < 0.001). In addition, linear regression (Figure 2) showed that 6RM squat load was a significant (p < 0.001) predictor for the deadlift, leg press, lunge, and step-up. The respective prediction equation was presented in Table 2. Results of the crossvalidation procedure using the PRESS statistic indicated that the predicted and actual loads were similar (Table 2).

Table 2

Table 2

Figure 2

Figure 2

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Discussion

The first major finding in the present investigation was that high correlations existed between the 6RM load of the bilateral squat and lower-body exercises (both bilateral and unilateral) in high-performance Karate athletes who predominantly perform unilateral movement (Table 1). The present study also found that the 6RM squat load was a significant (p < 0.001) predictor for the deadlift, leg press, lunge, and step-up (Figure 2). Moreover, linear regression equations were developed to determine the loads for the 4 lower-body exercises based on the squat load. Our results agreed with the findings reported by Ebben et al. (14) in that high explained variance (R2) was observed between squat and the lower-body exercises (Figure 2). Ebben et al. (14) reported that the squat accounted for 81, 62, and 71% of variance for deadlift, lunge, and step-up, respectively. Furthermore, it has been previously reported that the squat accounts for 55% of the variance in leg press (36), a value that is in close agreement with that observed (57%) in the present study (Figure 2).

However, in contrast to the findings of Ebben et al. (11) in collegiate athletes and recreationally active students, the present elite Karate athletes had heavier predicted loads in the lunge (70.39 vs. 66.82 kg) and the step-up (74.64 vs. 53.32 kg). It therefore appears that elite Karate athletes demonstrate superior performance in these unilateral exercises. This finding could be explained by an emphasis in training on performing unilateral striking actions. Indeed during sparring and fighting, Karate athletes perform mainly unilateral single-leg actions such as frontal (i.e., mae-geri), lateral (i.e., yoko-geri), and circular (i.e., mawashi-geri) kicks that heavily challenge balance, core muscles, and single-leg muscle strength and power (9,17,19,20,30). Stronger trunk and core muscle groups are necessary during unilateral exercises in stabilizing the body (7) during Karate performance (1,9,16,19,29,30,37) and may have contributed to greater stability and force output during lunges and step-ups. Therefore, the 6RM prediction equations must be specific to the population. For example, 6RM may be underestimated in elite unilateral-emphasis athletes when performing unilateral exercises and not induce a sufficient training effect, whereas measures may be overestimated in lower-level performers thereby increasing the risk of musculoskeletal injury.

Nevertheless, given the same 6RM squat load, (e.g., 100 kg), these results showed that elite Karate athletes have a similar predicted load in a bilateral activity such as the deadlift as compared with collegiate and recreational athletes (95.40 kg vs. 97.92 kg) (14). Thus, the high emphasis on stability or balance in Karate provides high correlations for both more (bilateral) and less (unilateral) stable resisted activities.

Leg extensions that are open kinetic chain exercise (31) were used by Ebben et al. (11) to examine the prediction ability of 6RM squat loads, whereas in the present study, a leg press was employed. Leg extension has been reported to induce higher shear force at the knee joint which stresses the anterior cruciate ligament (31). Moreover, a higher proportion of motor unit synchronization has been observed between vastus medialis obliquus and vastus lateralis in exercises such as the leg press, indicating better coordination within the quadriceps (27,34), and greater improvements in muscular strength and functional performance (2,40).

Finally, the measurements of the present study were performed in Karate athletes. The present results may not be representative of other high performance athletic groups and additional work on the use of squat testing to predict training loads for lower-body exercises is therefore necessary.

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Practical Applications

Previous studies have shown that some strength and conditioning coaches prescribe training loads for their high performance elite athletes via the subjective trial and error method because of limited time allocated to training and testing (13,15,32). However, this method is inaccurate and does not conform to the guidelines of National Strength and Conditioning Association (3). The squat is a major core strengthening exercise performed by elite athletes (12,13,15,32), but other forms of lower-body exercises with quadriceps as the prime mover induce different training effects on quadriceps, hamstrings, and gluteus muscles. The results of the present study demonstrate that coaches and fitness professionals when calculating 6RM loads for unilateral type exercises such as lunges and step-ups should be cognizant of the type of athlete involved. Previously published predictions of 6RM loads for lunges and step-ups based on collegiate and recreational athletes (11) were substantially lower than the loads predicted in the present study in elite athletes who predominantly use unilateral movements. Thus, the use of these equations has to be specific to the individual athletic population, otherwise loads could be either underestimated in elite athletes and not induce a sufficient training effect or overestimated in collegiate and recreational athletes increasing the risk of musculoskeletal injury. Karate and other martial art coaches and athletes should consider using these simple prediction equations when prescribing resistance training exercises to reduce training and testing time and ensure sufficient training effects.

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Acknowledgments

We would like to thank Miss Neng Azhanie Azman from the Nutrition Center, National Sports Institute of Malaysia for obtaining the skinfold measurements in the present study. The authors have no conflicts of interest that are directly relevant to the content of this article. Results of the present study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association. Competing interests and grant support: None declared.

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Keywords:

load estimates; resistance; strength; unilateral; bilateral

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