Athlete monitoring strategies are used to understand imposed training loads, and to evaluate an athlete's response to training stimuli. Monitoring strategies can be useful in optimizing an athlete's performance by determining their position on the recovery-adaptation continuum following training exposures, managing training loads to mitigate injury risk, as well as establishing quantitative parameters to guide return-to-play and return-to-performance protocols following an injury (Halson, 2014; Bourdon et al., 2017; Dunlop et al., 2019; Taberner et., 2019). Monitoring external training load (eTL) refers to the assessment of mechanical or locomotive work completed by the athlete and provides sport performance coaches with an objective measure of work performed during training, as well as games (Halson, 2014; Heishman et al., 2018a; 2018b; Fox et al., 2018; Svilar et al., 2018a; 2018b). Wearable microsensors, known as inertial measurement units (IMUs) offer a practical and convenient option to quantify eTL in indoor team sports, such as basketball (Holme, 2015; Fox et al., 2017).
IMUs have been used to characterize eTL among basketball athletes during both practice and competition, with PlayerLoad[TM] (PL) frequently reported as the key workload variable (Scanlan et al., 2014; Schelling and Torres, 2016; Aoki et al., 2017; Heishman et al., 2017; 2018a; 2018b; Peterson and Quiggle, 2017; Fox et al., 2018; Svilar et al., 2018a; 2018b). PL is a vector of magnitude, expressed as the square root of the sum of the squared instantaneous rate of change in acceleration in each of the 3 orthogonal planes, divided by the scaling factor 100 and expressed in arbitrary units (au) (Barrett et al., 2014; Heishman et al., 2018a; 2018b). The computation of PL includes the summation of load vectors in all 3 orthogonal planes (mediolateral, anteroposterior, and vertical), however laboratory evidence suggests the vertical component of PL contributes 50-60% of load accumulation, while the mediolateral and anteroposterior components only contribute 20-25% of load accumulation during PL analysis (Barrett et al., 2014). Field-based analyses have identified strong correlations between PL and total distance traveled, suggesting the sensitivity of PL to running based activity, likely resulting from increased vertical accelerations from ground reaction forces during the gate cycle (Cormack et al., 2013; Barrett et al., 2014; Polgaze et al., 2015). McLean et al. (2018) speculated that an abundance of vertical acceleration data may mask smaller increases in mediolateral and anteroposterior vector activity, which may be pertinent to the sensitivity of eTL quantification. Moreover, it may be speculated that the large vertical component of basketball play (Schelling and Torres, 2016; Stojanovic et al., 2018) could exacerbate the suppression of small increases in mediolateral and anteroposterior movements, such as increases associated with change-of-direction (CoD) activity. These findings have spawned contemporary interests among practitioners to determine alternative strategies for quantifying cumulative movement, such as 2-Demensional PL ([PL.sup.2D]), that only includes the mediolateral and anteroposterior movements, as well as the evaluation of the each individual PL vector, however these analysis have yet to be performed in basketball.
In addition to quantitating work performed during training, some athlete monitoring strategies are used to evaluate the response of the athlete to the training imposed. The countermovement jump (CMJ) is commonly used to evaluate neuromuscular readiness and performance in sport (Aoki et al., 2017; Rowell et al., 2017; Heishman et al., 2018a; 2018b; Ferioli et al., 2018) and may provide insight regarding the capacity of an athlete to recover from training. Interestingly, previous research has reported increases (Aoki et al., 2017) and decreases in CMJ height over the preseason among professional basketball players, (Ferioli et al., 2018) decreases in collegiate players, (Heishman et al., 2017) while semi-professional athletes have revealed no change (Ferioli et al., 2018). These results may reflect the level of play or varying levels of eTL, which often go unquantified. Previous basketball literature has evaluated changes in CMJ height, while evidence from alternative sports suggests that different force-time characteristics may accentuate fatigue by identifying compensations in movement strategy to achieve the desired gross output (Cormack et al., 2008; Gathercole et al., 2015; Rowell et al., 2017). Of note, Flight Time to Contraction Time Ratio (FT:CT) evaluates the athletes' jumping strategy and has recently been established as a reliable variable in collegiate basketball players (Heishman et al., 2018a; 2018b; 2019). Additionally, Reactive Strength Index Modified ([RSI.sub.Mod]), derived from dividing contraction time (CT) by jump height, provides an index of explosiveness (Kipp et al., 2016), and may also be a useful parameter to quantify changes in performance (McMahon et al., 2018; Heishman et al., 2019). Therefore, coupling eTL with resultant changes in CMJ performance may allude to the dose-response relationship of training. Although an acute inverse relationship between eTL and subsequent CMJ performance has been established (Heishman et al., 2018a; 2018b; Cruz et al., 2018), no data exists paralleling eTL with CMJ performance in basketball athletes.
Limited data exist identifying the influence of player position on eTL in collegiate basketball players. Similarly, no data exist examining the impact of a player's scholarship status, which alludes to their role on the team, on eTL. Furthermore, a paucity of literature is available relating eTL parameters with subsequent changes in CMJ performance parameters. Therefore, the purpose of the present study was to 1) characterize the average eTL per sesSion; 2) examine differences in the average eTL per session each week; and 3) explore changes in CMJ performance across the 5 weeks of preseason training phase in NCAA Division I basketball athletes. Subsequent analyses examined the influence of position and academic status on eTL. It was hypothesized that the average eTL per session would be similar across training weeks and that there would be a decrease in the neuromuscular performance indices of jump height, FT:CT, and [RSI.sub.mod] across the preseason.
Fourteen male (age = 19.7 [+ or -] 1.0 years, height = 1.98 [+ or -] 0.07 m, body mass = 94.7 [+ or -] 6.2 kg) NCAA Division I collegiate basketball players were included in this study. Participants were categorized into position groups consisting of forwards/centers (n = 7) or guards (n = 7) determined by the basketball coaching staff. Players were classified by academic status as either a scholarship or non-scholarship (Walk-on) athlete (Scholarship: n = 10; Walk-on: n = 4) and were active squad members of the University of Oklahoma's Men's Basketball team. This research was approved by the Institutional Review Board of the University of Oklahoma and all participants provided written, informed consent before participating in the study.
In a prospective observational study design, eTL was measured during 22 basketball practice sessions over the course of a 5-week preseason training phase. In addition, weekly measurements of neuromuscular performance were assessed using the CMJ, performed just prior to the start of each strength training session. Subjects performed 1 CMJ assessment prior to the start of the preseason (Pre) and then 1 CMJ assessment per week, following a day off from training, except for Weeks 2 and 3, where CMJ testing was performed in 2 separate sessions due to the logistics of strength training scheduling requiring a portion of the team to come 2 days after an off day. A detailed schedule is provided in Figure 1.
Figure 1. The schedule of practice, off-days, and CMJ assessments performed during the preseason. Practice = Team practice where external training load was monitored and practice always occurred following CMJ assessments. CMJ = countermovement jump assessment, followed by the (number) to identify the assessment, which always occurred prior to the start of strength training sessions; OFF = scheduled off day with no organized team training. Sunday Monday Tuesday Wednesday Thursday Week 1 OFF Practice Practice Practice OFF Week 2 OFF Practice Practice OFF CMJ (2) Practice Week 3 OFF Practice Practice Practice OFF Week 4 OFF Practice Practice Practice OFF Week 5 OFF Practice Practice Practice Practice Week 6 OFF CMJ (5) Friday Saturday Week 1 CMJ(1) Practice Practice Week 2 CMJ (2) OFF Practice Week 3 CMJ (3) CMJ (3) Practice Practice Week 4 CMJ (4) OFF Practice Week 5 OFF OFF Week 6 Procedures
External Training Load (eTL) Monitoring: Subjects wore the Catapult Sport OptimEye T6 IMU system (Catapult Innovations, Melborne, VIC, Australia) comprised of...