Maximal strength testing

The most common maximal performance measures used in past research within team sports are maximal strength assessments. Many maximal strength assessments have been used to monitor progress throughout training cycles (Argus et al., 2009; Beaven, Cook, et al., 2008; Comyns et al., 2010; Harris et al., 2008), yet few have focused upon maximal strength testing to measure fatigue (Haff et al., 1997). Much of the modern research using strength training to assess performance has rarely used standard measures of strength training, which, utilise percentage of one-rep maximum calculations (%1RM) and has instead used maximal isometric voluntary contraction (MVIC). The reason MVIC has been preferred to %1RM testing is that it determines the volitional force-generating capacity of a muscle under relatively standard conditions, whereas strength training does not. Recent support for the use of MVC for assessing EIMD was presented by Damas, Nosaka, Libardi, Chen, and Ugrinowitsch (2016) who noted MVC to be the best EIMD indirect marker, when researching retrospectively across 286 athletes. Additionally, traditional strength testing is fatiguing in nature while other maximal testing such as CMJ and MVIC are not and are therefore considered to be more applicable for use in elite team sport settings. MVIC assessment enables generation of a force-time curve, which can identify multiple markers of neuromuscular performance; yet contrasting support for the use of maximal strength assessment exists. Cairns et al. (2005) noted maximal strength as an invalid assessment for fatigue, due to the extent to which they replicate the nature of sports activities in question. Research by Verdijk, van Loon, Meijer, and Savelberg (2009), however, noted that 1RM strength tests represents a valid means to assess leg strength in humans, with

recommendations for using 1RM testing to assess changes in strength following an exercise intervention. The relevance of assessments of strength is that they could be applied to the fatigue testing proposed in this research.

As previously discussed, reliability of performance tests are of paramount importance for practitioners in order to ensure that the data collected is accurate and valid. Data within maximal strength testing have presented contrasting reliability, which was further supported by Soares-Caldeira et al. (2009) when assessing 1RM tests in adult women. Comfort, Jones, McMahon, and Newton (2015), by contrast, noted high test/retest reliability during the

isometric mid-thigh pull (IMTP), with >1.3% change in peak isometric force, > 10.3% in mRFD, > 5.3% in impulse at 100 ms, > 4.4% in impulse at 200 ms, and > 7.1% in impulse at 300 ms being considered meaningful, irrespective of posture adopted. Further support for the reliability (ICC > 0.90) of using isometric testing was noted by Bazyler, Beckham, and Sato (2015) with isometric squat noted as providing a strong indication of changes in strength and explosiveness during training. Recent research by Haff, Ruben, Lider, Twine, and Cormie (2015) presents an important consideration for practitioners, as the method used to asses RFD during an isometric mid-thigh clean pull (IMTCP) impacts on the reliability of the measure. Haff et al. (2015) did, however, acknowledge the reliability of the IMTCP (ICC 0.95, CV < 4%), thereby further supporting the use of isometric testing. Lastly an isometric posterior lower limb muscle test was reported by McCall et al. (2015) to be a reliable and sensitive measure to track match- induced fatigue in professional soccer players. This three second isometric contraction of the lower limb showed high reliability for dominant leg at 90° (CV = 4.3%, ICC = 0.95, ES = 0.15), non-dominant leg at 90° (CV = 5.4%, ICC = 0.95, ES = 0.14) and was sensitive enough to detect reductions in force for dominant leg at 90° (p = 0.0006, ES > 1) that could present valuable insights for future recovery practices in elite soccer.

Limited research exists regarding the magnitude of change of strength measures that signify fatigue, and as discussed previously, maximal strength testing is likely to induce fatigue and therefore should not regularly be implemented into elite settings. Recent research by Comfort and McMahon (2015) does, however, demonstrate high reliability for maximal strength implementation of the back squat (ICC = 0.994) and power clean (ICC = 0.997) performance in experienced lifters. From the research by Comfort and McMahon (2015) practitioners were advised to look for a change of > 5% in order to identify meaningful change in maximal strength back squat and power clean. Additional support for resistance training to measure readiness was, however, presented by Crewther et al. (2013) when assessing salivary testosterone and cortisol responses to resistance training workouts. They claimed that free testosterone responses to a midweek workout might provide an early sign of team readiness to compete. Despite support for the reliability of maximal strength testing to assess fatigue in rugby league players, contrasting evidence exists in research by Coutts, Reaburn, Piva, and Murphy (2007), who report minimal reductions in 3RM bench press and squat assessment during overreaching periods. This minimal change during overreaching periods, therefore, demonstrates a likely lack of support for the use of strength testing for assessing fatigue. Many of the other methods of performance testing critiqued within Chapter 2.4.1.2 and 2.4.4 (jump testing and biochemical testing) provide more detail and specific values that signify meaningful change, with rate of force development and variability in hormonal profile of rugby players in the days post-match providing more objective values than those reported for maximal strength.

In a review of models used to evaluate NMF, Cairns et al. (2005) discussed the use of mechanical fatigue measures using MVIC, such as isokinetic dynamometer exercises and dynamic knee extension, with research in rugby specifically conducted by Crewther et al. (2009) illustrating significant relationships between neuromuscular performance and hormone secretion patterns in elite rugby union. Within the research by Crewther et al. (2009) concentric mean and peak power during a 70-kg squat jump mean power (r = 0.41, p < 0.05), 50-kg bench press throw PP (r = 0.41, p = 0.05), and estimated %1RM strength for a box squat and bench press were positively correlated with salivary testosterone and cortisol concentrations. Another study using strength testing (3RM bench press and squat) to measure performance and readiness was that of Cook, Kilduff, Crewther, et al. (2014) who noted testosterone concentrations to be offset by morning training, thereby recommending morning based strength testing to improve afternoon performance in rugby union. Additionally, Johnston et al. (2013) supported the notion that upper body power is also a good indicator of NMF post rugby match and that upper body PP appears to be a suitable measure for the specific force related exertion involved in tackling. It is, however, important to note that time-course and mechanisms of fatigue of the upper body differ to that of velocity based lower body power movements.

From the research within this section it is clear that questionable validity and reliability exist within both maximal strength testing and MVIC testing. Due to these validity and reliability issues, along with the lack of access to facilities and manpower needed on a regular basis for both maximal strength and MVIC testing, these performance measures are excluded from future use within this research. Additionally, the equipment required for testing isometric

contractions (isokinetic dynamometers) are large in size and therefore cumbersome and expensive to use. Added to the fact that additional fatigue can be created as a result of both these forms of performance testing it is clear rationale to exclude their use within this research.