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Original Research

The Kansas Squat Test Modality Comparison: Free Weights vs. Smith Machine

Luebbers, Paul E.1; Fry, Andrew C.2

Author Information
Journal of Strength and Conditioning Research: August 2016 - Volume 30 - Issue 8 - p 2186-2193
doi: 10.1519/JSC.0000000000001404
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Abstract

Introduction

The ability to generate power is essential for success in many athletic endeavors (11). Therefore, the assessment of power is important for coaches and athletes who design training programs intended to increase power output. When resistance exercise is used for training lower-body power, the barbell back squat is often used. Common variants are done with either free weights (FW) or with a Smith machine (SM). As opposed to FW, which allow movement in multiple planes, an SM is a device in which the barbell is attached to stationary vertical supports, which restricts the barbell motion to within the frontal plane (3,6,28).

Although the general squatting motion is the same between FW and SM back squats, each variant has unique characteristics. The most obvious may be those afforded by the SM itself in terms of assistance or safety. Because the barbell is affixed to the vertical supports, it reduces the need for the athlete to balance the weight during the squat. This may allow the lifter to load additional weight to the bar because less effort is required to maintain its position (6). Additionally, if the SM has a lifter-initiated lockout feature (hooks attached to the barbell that can latch into notches integrated into the vertical supports), the perceived safety of the lift is increased (6).

Less obvious are the subtle differences in muscle activity that may occur during the squat because of the variances between the motions allowed for each lift. The FW back squat is similar to natural movement because it allows the athlete to move in all planes of motion during the eccentric and concentric phases of the exercise. The fixed barbell of SM does limit the natural motions of the athlete because the barbell is strictly maintained within the frontal plane throughout the lift.

Gutierrez and Bahamonde (10) presented information that indicated that the FW back squat allowed for greater range of motion (ROM) in the trunk and also in the hip, knee, and ankle joints. They noted that because of the fixed nature of the SM barbell, the forward knee motion of the participants during the exercise was more restricted than during the FW back squat, which may have led to the observed reduction in ROM. This supported earlier research by Abelbeck (1) who had demonstrated that variations in foot position during SM back squat resulted in differences in knee and hip movement. In 2005, Anderson and Behm (2) examined electromyographic (EMG) activity of select lower-body and trunk muscles. They found no differences between the FW and SM back squat on soleus, biceps femoris, abdominal stabilizers, or lumbosacral erector spinae activity. However, the vastus lateralis and upper lumbar erector spinae were more active during the FW squat compared with the SM squat, by approximately 29 and 14%, respectively. A similar study conducted by Schwanbeck et al. (29) monitored EMG activity of the tibialis anterior, gastrocnemius, vastus medialis, vastus lateralis, biceps femoris, lumbar erector spinae, and rectus abdominis. Contrary to Anderson and Behm (2), they found no difference in vastus lateralis activity but increased biceps femoris activation (26%) during the FW relative to the SM back squat. Additionally, they observed higher EMG activity in the gastrocnemius (34%) and the vastus medialis (49%) during the FW squat. No differences were seen in either the tibialis anterior or rectus abdominal muscles. Despite these, or perhaps in some instances, because of these differences, an SM is often used in training for power (13,19,22,26) and in assessing power development (5,9,15,18,19,21,22,25,30–32). Regardless of the reason, it is apparent that both FWs and SMs are used by many athletes and coaches.

The Kansas squat test (KST) is a repetitive lifting test that is capable of measuring indices of lower-body power (8,16). The KST is performed by completing 15 repetitions of a barbell back squat performed at maximal concentric velocity while initiating each repetition at 6-second intervals. Measures of power are determined through the use a Tendo external dynamometer tethered to the barbell. The KST has been shown to be a reliable measure of anaerobic power in recreational athletes (8) and a valid test of power in trained collegiate track and field power athletes (16).

The originators of the KST used a SM because it allowed them to have increased control over the gross motor pattern of the lift. Additionally, it was believed that the stability of the attached barbell in the SM would allow the lifter to exert maximal force without concern for balance (8). The follow-up research that established validity of the KST also used an SM in an effort to replicate the original procedures (16). The purpose of this study was to determine the feasibility of using FWs for the KST by comparing outcome measures with the established SM modality. Although previous work examining FW and SM modalities and protocols are not in entire agreement (2,6,10,29), it was hypothesized that the similarities between the 2 modes of back squat would be sufficient enough for the FW KST to be an acceptable alternative to the SM KST.

Methods

Experimental Approach to the Problem

This study investigated the feasibility of a FW KST modality by testing concurrent validity against the SM KST modality used in previous research (8,16). Correlations were examined between measures of lower-body peak power (PP), mean power (MP), relative fatigue index (FI) and posttest lactate (HLa). Paired samples t-test was also used to survey potential differences between the modalities. All participants completed the KST with both the FW and SM modalities.

Participants reported to the laboratory on 6 separate occasions across 3 weeks, during the track and field fall preseason. During the first week, the first 2 visits were for familiarization of the KST with the SM and with FWs. The third visit was for 1 repetition maximum (RM) testing using the SM. The second week of the study consisted of the fourth and fifth visits, which were the SM KST data collection tests at the beginning of the week and the FW 1RM toward the end of the week. The third and final week consisted of the sixth visit, which was the FW KST data collection test. With the exception of the familiarization sessions, testing for men and women were conducted on separate days (Figure 1). There were no dietary restrictions placed on the athletes at any time during the 3 weeks. Athletes were instructed to eat and drink as was customary.

Figure 1.
Figure 1.:
Familiarization and testing schematic.

Subjects

The track and field program was a part of the Intercollegiate Athletics Department at a regional university in the Midwest. The Institutional Review Board of the university granted permission to conduct the study. Recruitment of participants from the track and field team was agreed to by the coaching staff, in addition to allowing for the necessary modifications to be made to the athletes' practices on the days in which testing would take place. The principal investigator verbally explained the details of the study to the athletes at a squad meeting. In total, 23 athletes from the sprinters and jumpers squad volunteered to be participants (mean ± SD: weight, 69.7 ± 10.6 kg; age, 20.1 ± 1.1 years). The group consisted of 13 male (weight, 77.5 ± 6.7 kg; age, 20.0 ± 1.2 years) and 10 female (weight, 59.5 ± 3.4 kg; age, 20.3 ± 0.8 years) subjects. All volunteers had a minimum of 1-year training experience with the barbell back squat. An institutionally approved informed consent document was signed by each volunteer, and all were deemed healthy and able to participate by the university's medical and athletic training staff.

Procedures

Familiarization

Participants reported to the laboratory on 2 separate occasions for familiarization of the KST with the SM and with FWs. Because of time constraints, the men and women completed the same KST modality familiarization sessions on the same days (Figure 1). Because these sessions took place before the 1RM tests that would be used to determine the KST barbell loads and KST system loads for the actual data collection, KST barbell loads for the familiarization sessions were calculated using each athlete's FW back squat 1RM value that had been obtained in track practice during the previous weeks.

Additionally, at the request of the coach, these familiarization sessions were conducted throughout the track practice, to minimize lengthening practice time as much as possible. On both days, after the standard team warm-up, the athletes with the 2 lowest 1RM values reported to the laboratory for their familiarization sessions. As each athlete completed his or her session, he or she would return to the track, and the athlete with the next highest 1RM would leave practice and report to the laboratory. This process continued until all athletes completed the familiarization process.

Testing and Data Collection

To ensure that athletes would be in a rested, nonfatigued state for data collection, all other sessions, including the 1RM testing sessions and the KST modality testing sessions were completed immediately after the standard team warm-up and before any actual workout. The men and women were also tested on separate days (Figure 1).

One Repetition Maximums

SM-1RM Squat Procedures

Following strength-test protocols set forth by Kraemer et al. (14), participants completed a 1RM back squat test on a PSM144X Smith machine (Body-Solid Incorporated, Forest Park, IL, USA). As had been done in previous research (8,16), the foot placement of each participant during the 1RM was measured using a marked grid, which was located at the base of the SM. This helped ensure that participants used the same stance during the 1RM and the KST testing sessions.

FW 1RM Squat Procedures

The procedures for the FW 1RM were identical to the SM 1RM with the exception that they were performed using FWs rather than a SM.

The Kansas Squat Tests

KST Barbell Load and KST System Mass Calculations

The barbell load for the KST was determined using 70% of the participant's 1RM system mass, minus the body mass (BM) of the participant {([BM+1RM] × 0.70) − BM}. The KST system mass (i.e., the value input into the Tendo unit for power analyses) was found by summing the athlete's body mass and the KST barbell load (BM + KST barbell load). An example of these calculations can be found in Table 1.

Table 1.
Table 1.:
KST barbell load and KST system mass calculations.*
SM KST Procedures

A Tanita WB-3000plus Digital Physicians Scale (Tanita Corporation of America, Inc., Arlington Heights, I, USA) was used to measure the body mass of each participant before the test. A test-specific warm-up with FW barbell squats for 3 sets of 5 repetitions (1 × 5 at 30% 1RM, 2 × 5 at 50% 1RM) (8,16) was completed as well. The KST was performed in an SM with the calculated KST barbell load (Table 1). Foot placements from the 1RM tests were replicated. The depth of each repetition was monitored with the use of a Safety Squat monitor (Bigger Faster Stronger, Salt Lake City, UT, USA), which was strapped around the participant's right leg at the approximate midpoint of the thigh (16). The KST consisted of 15 speed squat repetitions at a cadence of 1 lift·per 6 seconds. The pace of the cadence was kept by a digital timer (Chronomix, Sunnyvale, CA, USA), which was programmed to countdown from 6 seconds and automatically repeat the sequence 15 times. The timer provided participants with both a visible display of the cadence and an audible beep each time a new repetition was to begin. The timer was started by the investigator as soon as the first repetition began. Each repetition consisted of lowering the weight in a volitionally controlled manner until the safety squat device emitted a tone, indicating that sufficient depth had been achieved (i.e., anterior thigh parallel with the ground). After a brief pause, the participant maximally accelerated upward through the concentric phase of the squat. Participants were instructed not to jump or raise their heels off of the ground. The next repetition began when the timer beeped and started a new countdown. This pattern was followed until the 15 repetitions were completed.

Power output during the KST was measured using a Tendo external dynamometer (Fitrodyne; Tendo Sports Machines, Trencin, Slovak Republic) (12) and the Tendo Weightlifting Analyzer software program (Fitrodyne; Tendo Sports Machines, Trencin, Slovak Republic). The software recorded the linear velocity of the dynamometer's tethered thread, which was attached to the end of the barbell, as it moved through the ROM of each KST repetition. As in the previous KST studies, calculations from the collected data and the participants' KST system mass (Table 1) were used to determine mean repetition power (8,16). Fry et al. (8) provides a detailed discussion on these calculations.

FW KST Procedures

The procedures for the FW KST were identical to the SM KST with the exception that they were performed using FWs and that the system mass was determined using the data from the FW 1RMs.

Lactate

Blood Lactate Analysis

As was done in the previous KST research (8,16), blood lactate was measured to compare the physiological response of the anaerobic energy system between both versions of the KST. A handheld Lactate Scout (SensLab, Leipzig, Germany) was used to analyze each participant's finger prick blood samples, which were taken just before the warm-up and approximately 5 minutes after test.

Statistical Analysis

Pearson correlation coefficients and paired samples t-tests for PP, MP, and relative FI were performed to examine the relationship between the FW KST and the SM KST and also the posttest blood lactate (HLa) values from each assessment. PASW Statistics 18 (SPSS Inc., Chicago, IL, USA) was used for analysis, and the level of significance was set at 0.05 for all tests.

Results

Kansas Squat Test

Concurrent validity was determined by correlating the outcome variables between the FW KST and the SM KST. When all athletes were examined together as a single group (N = 23), correlation coefficients indicated that there were significant relationships between the FW KST and the SM KST on measures of peak test power (r = 0.955; p < 0.01; Figure 2) and mean test power (r = 0.959; p < 0.01; Figure 3) but not for relative fatigue (r = −0.198; p = 0.364). The posttest lactate response also lacked a significant relationship (r = −0.109; p = 0.619). When examined in subgroups by gender, significant relationships were present in men (n = 13) but not in women (n = 10).

Figure 2.
Figure 2.:
Comparison of peak power for the free weight KST and the Smith machine KST (N = 23). KST = Kansas squat test.
Figure 3.
Figure 3.:
Comparison of mean power for the free weight KST and the Smith machine KST (N = 23). KST = Kansas squat test.

Paired samples t-tests indicated that while peak power and mean power were significantly higher for the FW KST (p ≤ 0.01), there were no differences between the FW KST and SM KST in relative fatigue and lactate (p ≥ 0.05), when all athletes were examined as a single group. These significant differences between test measures were similar in the gender subgroups as well.

One Repetition Maximums

Correlation coefficients between the FW 1RM and SM 1RM indicate a significant association when examined as the entire squad (r = 0.952; p < 0.01; Figure 4). This significant relationship was also observed in both gender subgroups.

Figure 4.
Figure 4.:
Comparison of 1 repetition maximum for the free weight and Smith machine (N = 23).

The SM 1RM was significantly higher than the FW 1RM when examined by paired samples t-test (p ≤ 0.01). The SM 1RM was significantly higher for both the men and women subgroups as well. Complete results of the total squad and gender subgroups are in Table 2.

Table 2.
Table 2.:
Comparisons of performance variables (mean ± SD) for the FW KST and the SM KST.*

Discussion

The purpose of this study was to determine the feasibility of a FW KST modality by comparing it against the SM KST (8,16). Based on the previous work examining SM back squats (1) and comparing FW and SM protocols (2,6,10,29), it was hypothesized that the similarities between the 2 back squat modalities would be sufficient enough for the FW KST to be an acceptable alternative to the SM KST.

When examining the correlations between the KST modalities on peak test power (r = 0.955; p < 0.01) and mean test power (r = 0.959; p < 0.01), they were sufficiently strong enough to indicate that the FW KST is concurrently valid and capable of providing comparable assessment of the SM KST peak and mean power. However, although this significant relationship remained for the men when data were analyzed in gender subgroups, the association weakened considerably for the women. One possible explanation for this could be differences that have been observed between genders during squat exercises. In 2010, Dwyer et al. (7) found that when compared with men, women tended to have smaller degrees of knee flexion and larger degrees of hip extension angles during lower extremity exercises, such as nonloaded single-leg squats and lunges. In addition, the women had higher levels of muscle activation in the rectus femoris and gluteus maximus relative to the men. Although the unilateral exercises used in the study are not direct comparisons with either FW or SM bilateral squats, they are indications that there are possible gender differences during the squat movement. Similarly, in 2 separate studies, McKean et al. observed that men and women exhibit different movement patterns during the squat exercise, possibly because of dissimilar lumbar and sacrum movement (24) and potential differences in lower limb length (23).

Because both the men and women demonstrated significantly high correlations between the FWs and SM for the 1RMs in the present study, these potential structural and kinematic gender differences may not play a large role during single-repetition maximal strength exercise. However, as the significant correlation between the 2 modalities for the KST was only observed for the men subgroup, and not for the women, this may indicate that these gender differences may play a role during multiple-repetition speed or power squats, such as those used for the KST.

Although the correlations between the 2 testing modalities were very strong, the paired t-tests indicated a difference in the outcome measures. For both PP and MP, athletes produced higher values with the FW KST than with the SM KST. This was observed for the entire squad and both gender subgroups (Table 2). A potential reason for this is that the FW 1RMs were lower than the SM 1RMs (see discussion below). The lighter load allowed the athletes to move the barbell at a higher velocity during the concentric phase of the lift during the FW KST than during the SM KST. Paired t-test of the mean velocity of each modality supports this because the FW KST mean velocity was significantly higher than that of the SM modality (Table 2). So although the athletes were moving less mass during the FW KST, the ability to move that mass at a greater velocity resulted in a higher power output.

Although strong correlations between indices of power were observed, there were only very low, nonsignificant relationships between the 2 modalities for relative fatigue and for posttest lactate concentration. Interestingly, t-tests between the FW KST and SM KST on both of these measures indicated that there was no difference between the 2 tests. This was found for the entire squad and gender subgroups (Table 2).

The relative fatigue index is an indication of the decrease in power output by the athlete during the test. That is, highest repetition power to lowest repetition power (8). Although the t-test indicates that there is no difference in relative fatigue between the 2 modalities, the low correlation suggests that athletes do fatigue differently in each test. Posttest blood lactate concentration for both modalities were similar to those observed in previous SM KST studies (8,16), both found the lactate to be significantly lower than that after a Wingate anaerobic test (WAnT). This suggests that the SM KST relies more on the phosphagen energy system than on anaerobic glycolysis (8,16). As with relative fatigue, the t-test indicates no difference in anaerobic metabolism between the FW KST or SM KST. Yet, low correlations indicate that the athletes' energy pathways may differ between protocols. Both of these factors (fatigue and energy production) could be the result of individual variation in muscle use and activity between FW and SM protocols (2,4,6,27,29).

Although comparing 1RM back squats results between FW and SM was not an expressed purpose of this investigation, a brief discussion is warranted. Cotterman et al. (6) determined that although there was no difference between FW 1RM and SM 1RM back squat in men, women performed better with the SM. The current study partially supports that finding in that the women also performed better with the SM rather than FW for their 1RMs. However, in contrast, the men also produced greater 1RMs with the SM. Research has demonstrated that stability does seem to influence muscle force production. McBride et al. (20) observed 45.6% reduction in peak force, 40.5% lower rate of force development, and more than 30% reduction in agonist muscle activity during isometric squat exercise when done on an unstable platform. Other researchers have reported similar reductions in indices of lower-body strength under conditions of decreased stability (2,4,27), although some investigations have produced mixed results (6,29). As yet, there may not be sufficient data available to provide a definitive answer to the extent that the stability of an SM may or may not influence squat performance. However, the current study suggests that it may be enough to allow increased back squat performance relative to FWs.

In conclusion, these data indicate that the FW KST is a valid and feasible alternative to the SM KST for assessing peak and mean test power for track and field sprinters and jumpers, although consideration may need to be given to female athletes. Additionally, the 2 test modalities demonstrate a slightly negative association in their measures of fatigue rate. When this is considered along with the low association between the participants' posttest lactate concentrations, it could be suggested that the 2 modalities address metabolic energy factors differently.

Practical Applications

As was discussed in previous research, relative to the WAnT, the KST is a more practical test for assessing lower-body power (16). The KST can be conducted in a weight room using equipment and an exercise with which many athletes are already familiar. Although the dynamometer does have a cost, it is generally more affordable relative to the WAnT-specific equipment. Also, in contrast, the dynamometer is not limited to use with the KST; it can be used in training athletes in various other ways (17).

The current study increases the practicality of the KST by demonstrating that results similar to the SM KST results can be obtained with the use of FWs. This removes the potential expense, which may have been necessitated by the requirement of an SM. Or, it simply gives the athlete and the coach an additional option for conducting the KST. However, because it seems that the choice of modality may result in different power output measurements, it would be important to exclusively use either the SM KST or the FW KST when using the test to track the progress of a power training program.

Acknowledgments

The authors thank the Emporia State University track and field team and coaches for their time and efforts in this study. They also express their gratitude to Brandon Toothaker for his assistance with data collection.

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Keywords:

assessment; resistance; specificity; strength; training

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