Relevance of Isometric Strength Assessments in Sports

Brief Overview

Muscular strength is an important physical attribute that underpins athletic performance (Suchomel et al., 2016; Stone, 1993). Greater muscular strength is associated with a greater rate of force development (RFD), muscular power, and better performance in sports skills such as sprinting, jumping and change of direction (Suchomel et al., 2016; Stone, 1993). In addition, improvements in strength have been shown to positive transfer to improved performance in a variety of other Olympic sports (Lum & Barbosa, 2019) strength training interventions. Furthermore, athletes at higher competitive levels tend to possess greater levels of strength then athletes at lower competitive levels (Baker & Newton, 2008). Hence, monitoring maximum strength progression is often part of athletes’ performance programme, and also used for other purposes such as talent identification and monitoring training readiness. 

Assessments that are often used to assess maximal strength are generally classified as either isometric or dynamic strength assessments (Beckham et al., 2013; Haff et al., 2015). Isometric strength testing (IsoTest) involves an athlete exerting force against an immovable device or bar while adopting specific joint positions. The forces generated are measured with either a strain gauge, cable tensiometer, dynamometer, load cell or a force plate (Figure 1) (Lum et al., 2020) that allow for the quantification of peak force or torque. In addition to peak force or torque, IsoTest also allows for the quantification of other force-time characteristics including time specific force values, RFD and isometric impulse (subject to the device) over intervals typically ranging from 50-300 ms (Lum et al., 2020). The ability to examine these force-time characteristics over critical time periods is an important strength of IsoTest as these measures are considered to be important physical attributes for performance of ballistic movements. As such, in this article, Danny Lum will discuss the reasons for the increased adoption of IsoTest and its relevance in high performance and clinical settings.

Why Isometric Test?

One reason for the increase in popularity of IsoTest could be because, in comparison to the commonly used 1 repetition maximum (1RM) test that is traditionally used to assess athletes’ muscular strength, IsoTest are relatively simple to administer, poses minimal injury risk, have high test-retest reliability, are able to detect subtle changes in strength and are less fatiguing (Lum et al., 2020). In addition, performing the 1RM test in isolation may not sufficiently assess the benefits of strength training (Buckner et al., 2017; Mitchell et al., 2012), and may fail to provide any insight into the rapid force production characteristics of athletes. For example, it was previously reported in a study that increases in 1RM strength were higher after training at 80% 1RM than at 30% 1RM (Mitchell et al., 2012). However, no differences in the change in RFD, and ability to exert maximal force at various time dependant epochs, were observed when participants were assessed using the isometric leg extension. It was also reported in a recently published review study that strength assessed by IsoTest and 1RM test do not increase in proportion after a period of resistance training intervention (James et al., 2023). One possible reason for this is that the training interventions often include the exercise used for the 1RM test. The greater increase in 1RM test than IsoTest performance could be attributed to better movement efficiency and motor control for the specific exercise. As IsoTest requires less complex motor control, any improvement in peak force assessed by this method is more likely due to improvement in force generation capability of the musculotendinous unit rather than improved movement efficiency. Hence, being a less skill-dependent assessment method, the inclusion of IsoTest may provide greater insights on the adaptations to a specific training programme.  

In recent years, more studies on multi-joint IsoTests have reported significant small to large relationships between force-time characteristics obtained from this mode of test and sports related dynamic performance (Lum et al., 2020) (Figures 2-5) (Supplementary Tables 1-4). These findings may have motivated practitioners to adopt the IsoTest as a monitoring tool as they have come to realise how force-time characteristics obtained from IsoTest can provide insights on the strength required for their respective sports performance. I shall briefly summarise the findings of these studies in the following sections.

Relationships Between Upper Limb Isometric and Dynamic Tests Measurements

The isometric bench press (IBPress) (Figure 2) is the most studied upper body IsoTest used to assess the upper limb pushing ability (Loturco et al., 2016; Murphy et al., 1994; Young et al., 2014). Researchers studying IBPress have mainly got their participants to perform the test at 90^o and120^o elbow angles. It was reported that IBPress is a highly reliable test for assessing peak force (ICC = 0.79 -0.98), but is not reliable for assessing RFD (ICC = 0.28-0.82) (Murphy et al., 1994, Young et al., 2014). One of the possible reasons could be because IBPress is performed while lying on a bench with padding. The rate of transmission of force via the bench to the forceplate is likely to be affected due to the padding’s property. For example, a bench with a softer padding may dampen the force more than one with a dense padding. Nevertheless, peak force obtained from IBPress has been reported to have moderate correlation to 1RM bench press (r = 0.570 to 0.78), with peak force obtained from a position closer to where concentric phase of dynamic bench press occurs having larger correlation (Baker et al., 1994; Murphy et al., 1994; Murphy et al., 1995). Furthermore, IBPress peak force was also reported to be correlated other measures of upper limb strength such as bench throw (r = 0.67 to 0.72) (Murphy et al., 1994), and sprint kayaking time (r = -70 to -0.75) and power (r = 0.74 to 0.79) (Lum & Aziz 2020b).

Another upper limb IsoTest that is increasingly being used is the isometric bench pull (IBPull) (Lum & Aziz 2020a; Lum& Aziz 2020b; Lum et al., 2021) (Figure 3). Similar to IBPress, researchers studying IBPull have mainly got their participants to perform the test at 90^o and120^o elbow angles. The IBPull was reported to have a very high correlation with 1RM bench pull (r = 0.833 to 0.858). It was also reported that when peak forces obtained from IBPull are input into Equation 1, the 1RM for dynamic bench pull can be predicted with a standard error of about 3% (Lum & Aziz 2020a). In addition, IBPull peak force was also reported to be correlated to sprint kayaking time (r = -0.83 to -0.88) and power (r = 0.83 to 0.86) (Lum & Aziz 2020b). 

Equation 1: 1RM bench pull = 0.039 × IBPull90 + 0.034 × IBPull120 + 19.605 

Collectively, results from studies indicated that both IBPress and IBPull are valid and reliable tests to assess upper limb strength. However, practitioners should note that the benches used for these tests may affect the test-retest reliability. Hence, it is important to use the same bench for repeated testing sessions.

Relationships Between Lower Limb Isometric and Dynamic Tests Measurements

The two IsoTests that are most studied and commonly used to assess the lower limb force generation capability of athletes are the isometric mid-thigh pull (IMTP) (Figure 4) and isometric squat (ISqT) (Figure 5). Studies that have examined the relationship between 1RM squat with ISqT (Bazyler et al., 2015; Blazevich et al., 2002; Drake et al., 2018; Tan & Lum 2024) and IMTP (McGuigan et al., 2006; McGuigan et al., 2010; McGuigan & Winchester 2008; Nuzzo et al., 2008; Requena et al., 2009; Townsend et al., 2017; Wang et al., 2016; Young & Bilby, 1993) have reported significant correlations between the 1RM back squat and the peak force obtained from ISqT (r = 0.688 to 0.940) or IMTP (r = 0.705 to 0.970) (Bazyler et al., 2015; Nuzzo et al., 2008; Wang et al., 2016).  In addition, in our recent publication, we reported that 1RM squat can be predicted by inputting peak forces obtained from ISqT at 60^o, 90^o, and 120^o knee angles into Equation 2 and 3 for male and female, respectively (Tan & Lum, 2024). The predicted 1RM showed 0.2±9.8% and 0.02±9.7% difference from the actual 1RM squat for male and female, respectively. These findings suggest that the peak forces measured from both ISqT and IMTP are valid metrics for assessing lower limb strength. 

Equation 2: 1RM squat = -25.605 + 0.039 x ISqT60 + 0.035 x ISqT90 + 0.007 x ISqT120

Equation 3: 1RM squat = 1.177 + 0.077 x ISqT60 – 0.013 x ISqT90 + 0.004 x ISqT120

Similarly, force-time characteristics such as peak force, RFD and force epochs (100-250 ms) obtained from ISqt and IMTP have also been reported to have significant correlation to sports related dynamic movements such as jumping (r = 0.346 to 0.820), sprinting (r = -0.480 to -0.790), change of direction (r = -0.510 to -0.657), sprint kayaking (r = -0.440 to -0.670) and cycling (r = -0.490 to -0.550) (Lum et al., 2020). Thus, assessing the force generation capability of athletes using ISqT and IMTP may provide practitioners with insights on the strength that athletes possess that are important for the performance of the above-mentioned sports related movements.

While both ISqT and IMTP are valid and reliable assessment methods for lower limb strength, peak force obtained from ISqT may be higher than IMTP when performed at the same joint positions, especially in female athletes (Brady et al., 2020). Hence, ISqT may be a better option to assess the max force generation capability of females. If IMTP were to be used, it is important that lifting straps are used to minimise the limitations of the athletes’ grip strength.  

Recommendations on Performing Isometric Tests

In this section, I will highlight several points that practitioners should take note while using IsoTests to assess their athletes force generation capabilities.

1. The relation between peak force obtained from an IsoTest and force generated from a specific movement is highest when the IsoTest is performed at the position where concentric phase is initiated for that specific movement. For example, peak force obtained from ISqT at ~60^o knee angle will have a higher relation to 1RM load of a parallel squat then ISqT performed at either 90^o or 120^o knee angle.
2. In order to obtain reliable results for IBPress and IBPull, it is important to perform the test on the same bench as the hardness of the padding may affect the force reading, especially for time dependent metrics.
3. When performing the IMTP, athletes should adopt a posture that reflects the start of the second pull of the clean, resulting in a knee flexion angle of 125-145^o, and hip flexion angle of 140-150^o (Figure 4), in their self-selected / preferred position. Athletes should hold on to the bar with elbows fully extended and lifting straps should be used (Comfort et al., 2019). 
4. During the attempts where the objective is to assess the RFD or early force development, the instruction to athletes should be to exert force “as fast and as hard as possible” and sustain the force for 1 s.
5. During the attempts where the objective is to assess the peak force, the instruction to athletes should be to exert force “as hard and as fast as possible” and sustain the force for 3-5 s depending on when the force starts dropping.
6. Ensure that there is limited pre-tension during the weighing period and no obvious countermovement prior to the initiation of isometric action.
7. Practitioners can take reference to Figure 6 and should visually inspect the force-time curves to determine whether their athletes should re-attempt the tests.

Conclusion

In conclusion, IsoTest are relatively simple to administer, pose less risk of injury, have high test-retest reliability, and are able to detect subtle changes in strength that dynamic tests may not be sensitive enough to detect. This mode of strength testing also allows for the analysis of force-time characteristics, such as RFD and force at critical time epochs, which underpin motion and sport specific tasks. It has been shown that IsoTest force-time characteristics were moderately to strongly correlated to dynamic performances of the upper and lower limbs as well as the performance of sports related movements. This indicates that IsoTest force-time characteristics are able to provide insights to the force production capability of an athlete for performing the movements mentioned in this blog. It is important to note that the best joint position at which IsoTest should be performed at would be the joint position at which concentric phase is initiated in the dynamic movement of interest. Finally, as IsoTests have lower motor control demand as compared to dynamic strength tests, it may provide a better gauge on actual muscular strength change than dynamic strength tests. With this in mind, practitioners can adopt this method to monitor the training progression of their athletes and evaluate the effectiveness of their training programmes.

References

Bellar D., Marcus, L., and Judge, L. W. (2015) Validation and reliability of a novel test of upper body isometric strength. Journal of Human Kinetics, 47(1), 189-195.

Bailey, C., Sato, K., Alexander, R., Chiang, C. Y., and Stone, M. H. (2013). Isometric force production symmetry and jumping performance in collegiate athletes. Journal of Trainology, 2(1), 1-5. 

Baker, D, G., and Newton, R. U. (2008). Comparison of lower body strength, power, acceleration, speed, agility, and sprint momentum to describe and compare playing rank among professional rugby league players. Journal of Strength and Conditioning Research, 22(1), 153-158.

Bazyler, C. D., Beckam, G. K., and Sato, K. (2015). The use of the isometric squat as a measure of strength and explosiveness. Journal of Strength and Conditioning Research, 29(5), 1386-1392.

Beattie, K., Carson, B. P., Lyons, M., and Kenny, I. C. (2017). The Effect of Maximal- and Explosive-Strength Training on Performance Indicators in Cyclists. International Journal of Sports Physiology and Performance, 12(4), 470-480.

Beckham, G., Mizuguchi, S., Carter, C., Sato, K., Ramsey, M., Lamont, H., Hornsby, G., Haff, G., and Stone, M. (2013). Relationships of isometric mid-thigh pull variables to weightlifting performance. Journal of Sports Medicine and Physical Fitness, 53(5), 573-581.

Berger, R. A., Herderson, J. M. (1966). Relationship of power to static and dynamic strength. Research Quarterly, 37(1), 9-13.

Blazevich, A. J., Gill, N., and Newton, R. U. (2002). Reliability and validity of two isometric squat tests. Journal of Strength and Conditioning Research, 16(2), 298-304.

Brady, C. J., Harrison, A. J., Flanagan, E. P., Haff, G. G., & Comyns, T. M. (2020). The relationship between isometric strength and sprint acceleration in sprinters. International journal of sports physiology and performance, 15(1), 38-45.

Buckner, S. L., Jessee, M, B., Mattocks, K. T., Mouser, J. G., Counts, B. R., Dankel, S. J., and Loenekke, J. P. (2017). Determining strength: A case for multiple methods of measurement. Sports Medicine, 47, 193-195.

Comfort, P., Dos’Santos, T., Beckham, G., Stone, M., Guppy, S., Haff, G. (2019). Standardization and methodological considerations for the isometric midthigh pull. Strength and Conditioning Journal, 41, 57-59.

De Witt, J. K., English, K. L., Crowell, J. B., Kalogera, K. L., Guilliams, M. E., Nieschwitz, B. E., Hanson, A. M., and Ploutz-Snyder, L. L. (2018). Isometric mid-thigh pull reliability and relationship to deadlift 1RM. Journal of Strength and Conditioning Research, 32(2), 528-533.

Dos’Santos, T., Thomas, C., Comfort, P., McMahon, J. J., and Jones, P. A. (2017a). Relationships between isometric force-time chracteristics and dynamic performance. Sports, 5(3), 68.

Drake, D., Kennedy, R., and Wallace, E. (2018). Familiarization, validity and smallest detectable difference of the isometric squat test in evaluating maximal strength. Journal of Sports Sciences, 36(18), 2087-2095.

Dumke, C. L., Pfaffenroth, C. M., McBride, J. M., and McCauley, G. O. (2010). Relationship between muscle strength, power and stiffness and running economy in trained male runners. International Journal of Sports Physiology and Performance, 5(2), 249-261. 

Haff, G. G., Carlock, J. M., Hartman, M. J., Kilgore, J. L., Kawamori, N., Jackson, J. R., Morris, R. T., Sands, W. A., and Stone, M. H. (2005). Force-time curve characteristics of dynamic and isometric muscle actions of elite women olympic weightlifters. Journal of Strength and Conditioning Research, 19(4), 741-748.

Haff, G. G., Ruben, R. P., Lider, J., Twine, C., and Cormie, R. (2015). A comparison of methods for determining the rate of force development during isometric midthigh clean pulls. Journal of Strength and Conditioning Research, 29(2), 386-295.

Haff, G. G., Stone, M., O’Bryant, H. S., Harman, E., Dinan, C., Johnson, R., and Han, K. H. (1997). Force-time dependent chracteristics of dynamic and isometric muscle actions. Journal of Strength and Conditioning Research, 11(4), 269-272.

James, L. P., Weakley, J., Comfort, P., & Huynh, M. (2023). The relationship between isometric and dynamic strength following resistance training: a systematic review, meta-analysis, and level of agreement. International Journal of Sports Physiology and Performance, 19(1), 2-12.

Kawamori, N., Rossi, S. J., Justice, B. D., Haff, E. E., Pistilli, E. E., O’Bryant, H. S., Stone, M. H., and Haff. G. G. Peak force and rate of force development during isometric and dynamic mid-thigh clean pulls performed at various intensitites. Journal of Strength and Conditioning Research, 20(3), 483-491.

Joffe, S. A., Phil, P., & Jamie, T. (2021). Maximal isometric force in the start of the first pull exhibits greater correlations with weightlifting performance than in the mid-thigh position in national and international weightlifters. The Journal of Sport and Exercise Science, 5(3), 202-211.

Khamoui, A. V., Brown, L. E., Nguyen, D., Uribe, B. P., Coburn, J. W., Noffal, G. J., and Tran, T. Relationship between force-time and velocity-time chracteristics of dynamic and isometric muscle actions. Journal of Strength and Conditioning Research, 25(1), 198-204.

Kraska, J. M., Ramsey, M. W., Haff, G. G., Fethke, N., Sands, W. A., Stone, M. E., and Stone, M. H. Relationship between strength characteristics and unweighted and weighted vertical jump height. International Journal of Sports Physiology and Performance, 4(4), 461-473.

Kuki, S., Kimitako S., Stone, M. H., Okano, K., Yoshida, T., and Tanigawa, S. The relationship between isometric mid-thigh pull variables, jump variables and sprint performance in collegiate soccer players. Journal of Trainology, 6(2), 42-46.

Leary, B. K., Statler, J., Hopkins, B., Fitzwater, R., Kesling, T., Lyon, J., Philips, B., Bryner, R. W., Cormie, P., and Haff, G. G. The relationship between isometric force-time curve characteristics and club head speed in recreational golfers. Journal of Strength and Conditioning Research, 26(1), 2685-2697.

Loturco, I., Nakamura, F. Y., Artioli, G. G., Kobal, R., Kitamura, K., Cal Abad, C. C., Cruz, I. F., Romano, F., Pereira, L. A., and Franchini, E. (2016). Strength and power qualities are highly associated with punching impact in elite amateur boxers. Journal of Strength and Conditioning Research, 30(1), 109-116.

Lum, D., & Aziz, L. (2020a). Validity and reliability of the isometric prone bench pull test. International Journal of Sports Medicine, 41(08), 520-527.

Lum, D., & Aziz, A. R. (2020b). Relationship between isometric force–time characteristics and sprint kayaking performance. International Journal of Sports Physiology and Performance, 16(4), 474-479.

Lum, D., & Barbosa, T. M. (2019). Effects of strength training on olympic time-based sport performance: A systematic review and meta-analysis of randomized controlled trials. International journal of sports physiology and performance, 14(10), 1318-1330.

Lum, D., Barbosa, T. M., & Balasekaran, G. (2021). Sprint kayaking performance enhancement by isometric strength training inclusion: a randomized controlled trial. Sports, 9(2), 16.

Lum, D., Haff, G. G., & Barbosa, T. M. (2020). The relationship between isometric force-time characteristics and dynamic performance: a systematic review. Sports, 8(5), 63.

Lum, D., & Joseph, R. (2019). Relationship between isometric force-time characteristics and dynamic performance pre-and post-training. The Journal of Sports Medicine and Physical Fitness, 60(4), 520-526.

Marcora, S., and Miller, M. K. (2000). The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function. Journal of Sports Sciences, 18(5), 313-319.

McGuigan, M. R., Newton, M. J., Winchester, J. B., and Nelson, A. G. (2010). Relationship between isometric and dynamic strength in recreationally trained men. Journal of Strength and Conditioning Research, 24(9), 2570-2573.

McGuigan, M. R., and Winchester, J. B. (2008). The relationship between isometric and dynamic strength in college football players. Journal of Sports Science and Medicine, 7(1), 101-105.

McGuigan, M. R., Winchester, J. B., and Erickson, T. (2006). The importance of isometric maximum strength in college wrestlers. Journal of Sports Science and Medicine, 5(CSSI), 108-113.

Lum, D., & Barbosa, T. M. (2019). Effects of strength training on olympic time-based sport performance: A systematic review and meta-analysis of randomized controlled trials. International journal of sports physiology and performance, 14(10), 1318-1330.

Lum, D., Barbosa, T. M., & Balasekaran, G. (2021). Sprint kayaking performance enhancement by isometric strength training inclusion: a randomized controlled trial. Sports, 9(2), 16.

Lum, D., Haff, G. G., & Barbosa, T. M. (2020). The relationship between isometric force-time characteristics and dynamic performance: a systematic review. Sports, 8(5), 63.

Lum, D., & Joseph, R. (2019). Relationship between isometric force-time characteristics and dynamic performance pre-and post-training. The Journal of Sports Medicine and Physical Fitness, 60(4), 520-526.

Marcora, S., and Miller, M. K. (2000). The effect of knee angle on the external validity of isometric measures of lower body neuromuscular function. Journal of Sports Sciences, 18(5), 313-319.

McGuigan, M. R., Newton, M. J., Winchester, J. B., and Nelson, A. G. (2010). Relationship between isometric and dynamic strength in recreationally trained men. Journal of Strength and Conditioning Research, 24(9), 2570-2573.

McGuigan, M. R., and Winchester, J. B. (2008). The relationship between isometric and dynamic strength in college football players. Journal of Sports Science and Medicine, 7(1), 101-105.

McGuigan, M. R., Winchester, J. B., and Erickson, T. (2006). The importance of isometric maximum strength in college wrestlers. Journal of Sports Science and Medicine, 5(CSSI), 108-113.

Stone, M. (1993). Position statement and literature review: explosive exercise and training. NSCA Journal, 15, 7-15.

Stone, M. H., Sanborn, K., O’Bryant, H., Hartman, M., Stone, M. E., Proulx, C., Ward, B., and Hruby, J. (2003). Maximum strength-power-performance relationship in collegiate throwers. Journal of Strength and Conditioning Research, 17(4), 739-745.

Stone, M. H., Sands, W. A., Carlock, J., Callan, S., Dickie, D., Daigle, K., Cotton, J., Smith, S. L., and Hartman, M. (2004). The importance of isometric maximum strength and peak rate-of-force development in sprint cycling. Journal of Strength and Conditioning Research, 18(4), 878-884.

Suchomel, T. J., Nimphius, S., and Stone, M. H. (2016) The importance of muscular strength in athletic performance. Sports Medicine 46(1),1419-1449. 

Tan, W. Z. N., & Lum, D. (2022). Predicting 1 Repetition Maximum Squat With Peak Force Obtained From Isometric Squat at Multiple Positions. Journal of Strength & Conditioning Research, 10-1519.

Thomas, C., Comfort, P., Chiang, C. Y., and Jones, P. A. (2015a). Relationship between isometric mid-thigh pull variables and sprint and change of direction performance in collegiate athletes. Journal of Trainology, 4(1), 6-10.

Thomas, C., Comfort, P., Jones, P. A., and Dos’Santos, T. (2017). A comparison of isometric mid-thigh pull strength, vertical jump, sprint speed, and change of direction speed in academy netball players. International Journal of Sports Physiology and Performance, 12(7), 916-921.

Thomas, C., Jones, P. A., Rothwell, J., Chiang, C. Y., and Comfort, P. (2015b). An investigation into the relationship between maximum isometric strength and vertical jump performance. Journal of Strength and Conditioning Research, 29(8), 2176-2185.

Tillin, N. A., Pain, M. T. G., and Folland, J. (2013). Explosive force production during isometric squats correlates with athletic performance in rugby union players. Journal of Sports Sciences, 31(1), 66-76.

Townsend, J. R., Bender, D., Vantrease, W. C., Hudy, J., Huet, K., Williamson, C., … & Mangine, G. T. (2019). Isometric midthigh pull performance is associated with athletic performance and sprinting kinetics in division i men and women’s basketball players. Journal of Strength & Conditioning Research, 33(10), 2665-2673. 

Uali, I., Herrero, A. J., Garatachea, N., Marin, P. J., Alvear-Ordenes, I., and Garcia-Lopez, D. (2012). Maximal strength on different resistance training rowing exercises predicts start phase performance in elite kaykers. Journal of Strength and Conditioning Research, 26(4):941-946.

Van Someran, K. A., and Howatson, G. (2008). Prediction of flatwater kayaking performance. International Journal of Sports Physiology and Performance, 3(2), 207-218.

Wang, R., Hoffman, J. R., Tanigawa, S., Miramonti, A. A., La Monica, M. B., Beyer, K. S., Church, D. D., Fukuda, D. H., and Stout, J. R. (2016). Isometric mid-thigh pull correlates with strength, sprint, and agility performance in collegiate rugby union players. Journal of Strength and Conditioning Research, 30(11), 3051-3056.

Wells, J. E., Mitchell, A. C., Charalambous, L. H., & Fletcher, I. M. (2018). Relationships between highly skilled golfers’ clubhead velocity and force producing capabilities during vertical jumps and an isometric mid-thigh pull. Journal of Sports Sciences, 36(16), 1847-1851. 

Wilson, G. J., Lyttle, A. D., Ostrowski, K. J., and Murphy, A. J. (1995). Assessing dynamic performance: a comparison of rate of force development tests. Journal of Strength and Conditioning Research, 9(3), 176-181.

Young, W. B., and Bilby, G. E. (1993). The effect of voluntary effort to influence speed of contrction on strength, muscular power, and hypertrophy development. Journal of Strength and Conditioning Research, 7(3), 172-178.

Young, K. P., Haff, G. G., Newton, R. U., & Sheppard, J. M. (2014). Reliability of a Novel Testing Protocol to Assess Upper Body Strength Qualities in Elite Athletes. International Journal of Sports Physiology and Performance, 9(5), 871-875.