MDS encompasses various sub-components, including perceptual factors, decision-making, and change of direction speed. Breaking down these components helps in identifying the specific cognitive, biomechanical, technical, and physical requirements of each task, enabling targeted training methods. Physical qualities like reactive strength, rate of force development (RFD), and peak force (PF) are crucial for achieving high and rapid braking and propulsive impulse, which are essential in changing direction, sprinting, and decelerating during MDS actions. These qualities underpin key MDS components such as deceleration, acceleration, and top-end speed (McBurnie and Dos’ Santos, 2022), providing athletes with advantages to outperform opponents. Assessing these physical capacities allows for evaluation and monitoring, facilitating a reverse-engineered approach to identify technique, biomechanical, and physical factors that contribute to MDS performance. A detailed evaluation of the physical demands of COD is provided in a previous post leading to the identification of important muscle strength qualities that should be considered for profiling the MDS athlete.
Best Practice
Fitness testing is crucial in assessing an athlete’s current fitness level and monitoring their progress during training and rehabilitation. It enables practitioners to identify strengths and weaknesses and tailor training, accordingly, optimising the use of time and resources for maximal performance gains and efficient rehabilitation. Regular testing provides vital information to athletes and support teams, aiding in monitoring program effectiveness, establishing baselines for post-injury progress, providing motivation, and identifying talent. Validity, reliability, and objectivity are essential principles in conducting effective tests that accurately reflect changes in an athlete’s fitness. Careful control and standardisation of procedures are necessary for repeatability and consistent progress monitoring.
Validity and Reliability
Validity refers to whether the test measures what it intends to measure. Some tests directly measure that which is required: what you see is what you get. For example, a 1 repetition maximum (RM) back squat provides an overall measure of maximal dynamic strength, whereas performing a 20RM would reflect muscular endurance. Both examples use the same test but manipulating the number of repetitions will change the physical quality tested. Therefore, practitioners should ensure that the test they are using is measuring the physical quality of interest. Reliability in fitness testing refers to the consistency and repeatability of scores across time or testers, with potential error sources including the measurement instrument, athlete, and tester. Researchers and practitioners should consider whether the tests they use can effectively detect genuine improvements in performance. This analysis is often overlooked but crucial for practitioners to determine the significance of training interventions. Factors like test validity, reliability and sensitivity must be considered, and establishing thresholds or utilising the signal-to-noise ratio can aid in interpreting and reporting testing data. Common measures of validity, reliability and sensitivity are provided in Table 1.
Deciding on Tests
The choice of tests should reflect the characteristics of both the sport and individual player position. When designing a fitness testing battery, several factors must be considered, including:
- How many tests? The number of athletes and the amount of time allowed will determine how many tests are feasible.
- What tests? Decision based on the needs analysis of the sport and the available equipment.
- What order? When conducting several tests, the performance of a previous test can impact the performance of a subsequent one.
- What equipment? The equipment should allow tests to be accurately reproduced and limit tester objectivity.
Laboratory Versus Field Testing
Exercise science traditionally categorised tests as laboratory-based or field-based. However, advancements in portable technology have blurred the lines between the two categories. In-ground force platforms are now portable, and wearable technology can assess metrics previously requiring expensive equipment. This trade-off can impact control, but there are ecological validity benefits. Test robustness is still essential, and practitioners need to ensure data validity and reliability.
Standardisation of Testing
Standardising test conditions each session is required for increasing test validity and reliability. Retesting should also be conducted under the same conditions. Although challenging, testers should be aware of potential factors impacting test results. Athletes must be provided a testing environment allowing them to perform at their best. Standardising test sessions requires considering several factors (Table 2).
Meaningful Metrics
After selecting the right assessments for the sport, the next challenge is to identify meaningful metrics to analyse and inform training. Many software packages return countless variables to feedback to the athlete, but practitioners should be mindful as to which variables are used to ultimately improve their athletes’ performance. These include:
- Relationship of the metric to performance (validity).
- Selecting a variable which has high reliability (low error) and is sensitive enough to detect “real” changes in performance.
- Variables which have good predictive capabilities (i.e., surrogate), or can discriminate between different playing standards /levels.
- To meet the needs of the sport and athlete, accurate data from literature and detailed observation are used to identify strengths, weaknesses, and injury risks, informing targeted training.
Practitioners should ensure that selected tests and their associated metrics help to inform practice. Figure 1 shows a summary of factors to consider for standardisation of testing physical qualities associated with MDS.
Assessment of Physical Qualities
Stretch-Shorten Cycle Function
Vertical jump tasks like the squat jump (SJ), countermovement jump (CMJ), and drop jump (DJ) are commonly used to assess lower body impulse in sports. Stretch-shortening cycle (SSC) performance is an important component in testing protocols, and appropriate tests should be selected based on ground contact times. CMJ is classified as a slow-SSC movement with ~800 milliseconds movement time (Suchomel et al., 2016), whilst the SJ test measures concentric performance. Various methods like reactive strength index (RSI), eccentric utilisation ratio (EUR), and pre-stretch augmentation (PSA) can be used to compare CMJ and SJ performance, with minimal differences observed between these methods (Suchomel et al., 2016). Guidelines will be provided on assessing SSC function, equipment, and protocols.
Equipment
Many options are available to assess SSC function, yet the choice will depend on the level of information required by the practitioner. Force platforms are considered the “gold standard” method to assess SSC function. Affordable and valid commercial force platforms have been recently developed, demonstrating high reliability (Lake et al., 2018). Other alternative (field-based) methods that are commercially available to practitioners are outlined in Table 3.
Force Platforms
The fundamental mechanical principle which force platforms adhere to is Newton’s Third Law of Reaction and this helps to associate the measured force with the force applied by the athlete (i.e., ground reaction force). Dependent on manufacturer, forces are measured directly in three planes (vertical, anterior-posterior, and medio-lateral). Inexpensive portable force plate systems have shown to record accurate measures of CMJ force-time variables, compared to laboratory-based systems (Lake et al., 2018). A possible limitation of such systems is that each platform is relatively small compared to laboratory-based platforms and may affect some athletes for some movements. Regardless of the type of force platform used to assess SSC function, there are common considerations which must be given to their set-up to increase the validity and reliability of resultant force-time data (Table 4).
Vertical Jump
SJ testing begins with an athlete performing a countermovement, which is then held for 2-3 seconds before vertically jumping. No differences in jump height between the self-selected and standardised SJ starting positions (Petronijevic et al., 2018), and both were highly reliable. On the other hand, that jump height is shown to increase with greater squat depths (McBride et al., 2010), but the time needed to complete the jump from a deeper position was longer, making it impractical for certain athletic populations.
CMJ testing for jump height has excellent reliability and requires limited familiarisation, particularly with athletes. Instructions have been shown to be vital during jump testing, with an external focus instruction of “push away from the ground as explosively as possible” resulting in greater jump height, peak velocity, and mean concentric velocity than an internal focus instruction (Talpey et al., 2016). Reactive strength index modified was found to be higher with instructions to “jump as fast as possible” compared to “jump as high and as fast as possible” (Sánchez-Sixto et al., 2021). Jumping with or without the use of the arms will impact on the results, with higher vertical jump height with arm swing. It may be the case that jump tests that utilise arm swing may be appropriate for certain sports and could increase the specificity of the test.
The depth of the countermovement is another testing consideration that can affect force-time variables. Higher jump heights are observed in jumps that start from a deeper squat position compared to jumps performed from a smaller squat depth (Gheller et al., 2015). In contrast, maximum force and power output are higher in jumps with a smaller squat depth. Encouraging the athlete to adopt their preferred countermovement depth appears to be the best practice from a reliability perspective and will provide the practitioner with an opportunity to quantify the athlete’s natural jump strategy.
Several trials should be conducted with jump assessments. Increasing trial size will in most cases reduce the typical error associated with a test variable. Recent work found taking the average of multiple trials resulted in lower coefficient of variation (CV) when compared to the best value of 8 CMJs (Kennedy and Drake, 2021), but it may be best to take the average from 2-3 trials to save on additional testing time. Using either the best or average performance may have a similar ability to monitor changes in jump performance (Al Haddad et al., 2015).
In conclusion, jump assessments are essential in evaluating an athlete’s physical abilities. Both SJ and CMJ testing are highly reliable and require limited familiarisation. It is important to consider the instructions given during testing, the use of arms during jumping, and the depth of the countermovement. Encouraging the athlete to adopt their preferred countermovement depth appears to be the best practice from a reliability perspective. Finally, it is important to conduct several trials to reduce the typical error associated with a test variable.
Reactive Strength
Drop jump testing is a valuable method to assess reactive strength and the ability to tolerate rapid stretch-shortening cycle (SSC) movements. The reactive strength index (RSI) is commonly used and can be calculated using contact time, flight time, or jump height (Flanagan et al., 2008). The flight time-to-contraction time ratio is another reliable method for athlete assessment (McMahon et al., 2018). It is important to use consistent methods and consider any differences with other approaches. The reliability of drop jump RSI has been demonstrated in various athlete populations.
Drop heights can be a single height or a profile of heights (Byrne et al., 2017; Moir et al., 2018), allowing coaches to build an individual reactive strength profile and evaluate stretch-load tolerance. However, technical competency should still guide the selection of an appropriate drop height during training.
Verbal instructions during drop jump performance can impact results. Specific instructions to maximise RSI can reduce contact time but also decrease jump height (Khuu et al., 2015; Young et al., 1995). Different instructions have varying effects on jump height and RSI. Instructing athletes to minimise ground contact time may affect jump height and increase loading rates.
Standardising the drop height is crucial, as variations have been observed compared to the intended height (Costley et al., 2017; Geraldo et al., 2019). Athletes should step out from the box instead of stepping down or jumping off it to ensure accurate testing. Alternatively, repeated jump tests like the 10/5 can be used to assess reactive strength while addressing the issue of height standardisation.
Testing Isometric Strength
Isometric muscle contractions, which do not involve joint movement, are used to assess maximal force production. While some studies question their usefulness (Wilson and Murphy, 1996a, 1996b), a recent review supports the relationship between isometric force-time characteristics and sprint/change of direction performance (Comfort et al., 2019). Isometric tests offer advantages such as ease of administration, high reliability, minimal familiarisation, shorter duration, and less fatigue compared to dynamic 1RM tests. They also correlate with performance in various dynamic strength tests. Key metrics in isometric testing include peak force, force at different time intervals, rate of force development (RFD), and impulse values. The force-time curve analysis enables quantification and monitoring of strength aspects. The commonly used tasks for assessing isometric force-time characteristics are the isometric mid-thigh pull (IMTP) and isometric squat.
Isometric Mid-Thigh Pull
The most commonly used isometric test with athletes is the Isometric Mid-Thigh Pull (IMTP) (Comfort et al., 2019; Stone et al., 2019, p. 25), which mimics the power position in weightlifting (Garhammer, 1993). IMTP peak force (PF) has high reliability, while other variables like rate of force development (RFD) are less reliable (Haff et al., 2015). Time-dependent epochs have shown better reliability (Haff et al., 2015) and relationships to dynamic performance measures. It is suggested that practitioners select specific testing protocols depending on whether they want to assess PF or RFD. Body position during the IMTP can influence force-time measures (Dos’Santos et al., 2017; Beckham et al 2018; Guppy et al. 2018;2019), but PF and time-specific force remain reliable regardless of position.
A standardised posture is recommended (Comfort et al., 2020), whereby depending on the athlete the exact knee and hip angle may vary and some angle adjustments may be necessary to optimise the individual athletes pulling position. Three review articles suggest that a minimum sampling frequency of 1000 Hz should be used when performing isometric assessments to ensure accuracy, especially in time-dependent variables such as time-specific force, RFD, and impulse (Comfort et al., 2019; Maffiuletti et al., 2016; McMaster et al., 2014). Instructions to focus on “pushing the ground as hard and as fast as possible” yield greater PF (Halperin et al., 2016). Verbal encouragement during testing is essential, but individual preferences should be considered. Portable systems, such as load cells (James et al., 2017), can be used as alternatives to force plates but may have uncertain reliability for certain variables. Isometric strength can be assessed in bilateral or unilateral conditions, both of which have shown reliability (Bailey et al., 2015; Dos’Santos et al., 2016).
Isometric Squat
Compared to the IMTP, the isometric squat produces greater peak force and impulse, making it a better option for determining maximum lower body force capacity (Brady et al., 2018), but its reliability is limited compared to the IMTP. Joint angle also affects resultant isometric squat metrics and reliability and should be standardised (Lynch et al., 2021; Palmer et al., 2018).
The isometric squat may require more familiarisation compared to the IMTP (Drake et al., 2018). As with the IMTP, constant tension should be applied to the bar prior to the initiation of the test (Bazyler et al., 2015). Excessive force production prior to the start of the test should be avoided as this will impact RFD values. Taken together, it is important that researchers and practitioners not use these tests interchangeably. Both tests are useful to be performed, yet practitioners should consider the demands of the sport and adopt a test that provides consistency in joint angles and subsequent reliability of key metrics to evaluate maximum isometric strength.
Testing Dynamic Strength
Another method for evaluating muscular strength is determining the maximum weight that can be lifted for a prescribed number of repetitions. When attempting to evaluate strength either the 1-RM, three RM (3-RM), or five RM (5-RM) tests are employed (McGuigan et al., 2013; Nimphius et al., 2012). If strength endurance is being evaluated the maximum weight that can be lifted for 8–12 RM tests may be evaluated. All tests are measures of the maximum amount of load lifted according to the correct technical specifications. The most common lower-body exercises tested are the back squat and power clean. When conducting these types of tests, it is important to consider the movement pattern, contraction type (i.e., eccentric-concentric, concentric only, eccentric only) and the warm-up strategy employed to prepare the athlete to give a maximal effort as these may impact the reliability of the test. Basic considerations for lower-body repetition maximum testing are presented in Table 5 whilst specific methods and protocols for conducting RM testing have been described previously (Haff, 2018; McGuigan, 2019).
Isokinetic Dynamometry
Isokinetic dynamometry allows the measurement of muscle strength (net muscle torque) for all joints of the body in most of their planar movements, at controlled speeds of movement (constant angular velocity), and in different modes of contraction (concentric, eccentric, and isometric). A main advantage of isokinetic assessment in relation to MDS is that eccentric knee extensor and flexor strength can be isolated and assessed linked to its role in the phases of COD, and subsequent profiling of the athlete. With the exception of Nordic Curls (Opar et al., 2013), there is a paucity of tests to assess lower-body eccentric strength. Yet, Nordic Curls are bilateral and do not quantify the maximal torque a hamstring group can produce (Wiesinger et al., 2020). It is beyond the scope of this article to discuss the use of isokinetics at length; therefore, thus the authors recommend reading the chapter by Baltzopoulos (2008) for a more detailed review.
Conclusion
The assessment of muscle strength qualities that underpin MDS is essential to identify strengths and weaknesses in an athlete’s physical profile to help individualise MDS development programmes. Several muscle strength qualities such as SSC function, maximal force, and RFD, concentric and eccentric strength may be considered important underpinning physical qualities for MDS actions and should be considered for assessment. Test options for these qualities have been outlined in this article, which is by no means an exhaustive list and other test options for these qualities may be available to better serve practitioners. Nevertheless, in designing and implementing a testing battery practitioners must carefully consider the standardisation, reliability, and validity of test protocols to ensure that the tests can precisely identify the athlete’s physical abilities and enable monitoring of these abilities against the goals of the training programme.
This blog is adapted from a book chapter in Jones, P.A., & Dos’Santos, T. (2023). Multidirectional speed in sport: Research to Application. Routledge.
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