Acute Neuromuscular and Endocrine Responses Following High and Low External Training Loads in Collegiate Basketball Players

Abstract

INTRODUCTION: Elite athletes undergo aggressive training regimens containing strategically induced fatigue in an attempt to maximize adaptation and performance improvements to meet the individual demands of the various sport. Athlete monitoring strategies are often used to track training loads and subsequent changes in performance. Inertial measurement units are often utilized to quantify the external training loads (eTL), also known as the biomechanical or locomotive stress, during indoor team sport activities, while the countermovement jump (CMJ) is employed to evaluate acute neuromuscular fatigue and performance. Little data exist examining the dose response of eTL and subsequent change in neuromuscular fatigue and performance, especially in basketball players. Additionally, although the CMJ is a commonly used field measure, exploring specific alterations in the CMJ force-time characteristics rather than gross output measures has been proposed to provide more insight with regards to changes in neuromuscular fatigue and performance compared to only considering gross output parameters, however this is yet to be explored among basketball players. PURPOSE: Therefore, the purpose of this dissertation was to examine the acute neuromuscular function and endocrine responses to High versus Low eTL basketball practices in a cohort of collegiate basketball players. A secondary aim sought to examine if neuromuscular alteration were primary central or peripheral in origin in response to a sport-specific basketball training session. METHODS: This dissertation was divided into two parts. Part I included 16 NCAA Division I basketball players (Male = 12; Female = 4) that performed a High and Low eTL practice, in a cross-over study design, where practice intensity measured using IMUs and intensity was characterized by PlayerLoad/minute (PL/min). Prior to each practice, participants provided a salivary sample used to assess testosterone, cortisol, and Testosterone:Cortisol ratio, as well as performed 3 CMJs on a dual cell force platform. At the conclusion of each practice, participants provided another salivary sample and perform 3 more CMJs. Participants returned 24-hours following practice to provide another salivary sample and perform 3 more CMJs. Perceived fatigue and muscle soreness were assessed using subject recovery questionnaires prior to practice and 24-Hours following practice. Part II include 15 NCAA Division I basketball players (Male = 9; Female = 6) underwent neuromuscular performance assessments before, immediately-after, and 24-hours following a team practice. The eTL of each practice was captured using an IMU. Maximal voluntary contraction (MVC) and twitch responses to electrical neuromuscular stimulation were assessed during the isometric knee extensor contraction and at rest to measure central (voluntary activation) and peripheral (twitch torque) fatigue, as well as responses in twitch torque at rest were used examine the prevalence of low frequency fatigue. In addition, participants performed 3 CMJs at each time point to characterize neuromuscular fatigue and performance. STATISTICAL ANALYSIS: Data normality was confirmed using descriptive and graphical information supplemented by the Shapiro-Wilk test statistic. In Part I, a 2-way (Sex [male, female]) × Condition [high load, low load)] repeated measures (RM) analysis of variance (ANOVA), evaluate differences in eTL. Data from the recovery questionnaire exhibited a non-normal distribution, therefore the equivalent nonparametric test was utilized. Friedman's non-parametric test was used to test for significant differences in the median rank scores across the different conditions and time points. A 3-way (Sex [male, female] x Condition [high load, low load) x Time [pre-, immediately post, 24 hours-]) RM ANOVA was used to assess sex, condition, and time main effects, as well as the interaction between Sex, Condition, and Time for each CMJ variable. Additionally, a 2-way (Condition × Time) RM ANOVA was also used to evaluate Sex × Condition, Sex × Time, and Condition × Time interactions, with significant interactions examined using a post-hoc pairwise comparison with a Bonferroni correction to isolate simple effects. In Part II, an independent T-Test was used to evaluate differences in Training Loads during practice between sexes. A 2-way (Sex [male, female] × Time [Pre, 24 hours-post exercise]) was utilized to evaluate difference in Recovery questionnaire parameters, with post-hoc pairwise comparison using Bonferroni corrections used when a significant difference was detected. A 2-way (Sex [male, female] × Time [Pre, immediately post, 24 hours-post exercise]) RM ANOVA was used to examine Sex and Time main effects and the interaction between sex and time for each variable: CMJ variables, MVC, voluntary activation, twitch characteristics and Low frequency fatigue. If a significant Sex × Time interaction was verified, the statistical model was decomposed by examining the simple effects with separate one-way repeated measures ANOVAs with Bonferroni correction factors for each group and time point. For both Part I and Part II, statistical significance was set at p  0.05. When comparing three or more groups, partial eta-squared (ηp2) effect sizes were calculated and interpreted as small (0.0099), medium (0.0588) and large (0.1379). When comparing between two groups, Cohen’s d (d) effect sizes were utilized and interpreted as trivial (0–0.19), small (0.20–0.49), medium (0.50–0.79), and large (≥0.80). RESULTS: In Part I, there were significant differences in eTL during the High compared to the Low condition, including PlayerLoad per Minute and PlayerLoad (p < 0.05), while there were no practical differences in duration. The high condition also exhibited significantly greater iTL response (p < 0.05). However, there were no differences in perceived responses between condition or across time (p < 0.05). No significant differences emerged for any CMJ variable between condition or across time (p < 0.05), however, 6 of 7 CMJ Tradition Variables, 4 of 6 CMJ Concentric Alternative Variables, 3 of 5 CMJ Eccentric Alternative Variables, and 3 of 7 CMJ Phase Duration Alternative Variables did display a small effect (d = 0.20-0.49) during the High condition from Pre to Post-practice, which was none of these effects were observed during the Low condition. Additionally, the majority of these variables that showed an effect following practice during the High condition, revealed trivial to no effect at the 24-hour assessment following practice, signifying a resolved back to baseline. There were significant sex differences in endocrine responses to eTL (p < 0.05). There were no differences in endocrine responses between the high or low eTL conditions (p > 0.0.5) 4) In men, there were significant increases in testosterone from Pre to Post-Practice that returned to baseline at 24-hour following practice (p < 0.05) and cortisol appeared to increase from pre to post practice, but also return to baseline 24-hours following practice. In addition, testosterone:cortisol ratio appeared unaffected by condition and across time (p < 0.05). In testosterone, cortisol and T:C ratio appeared unaffected between conditions and unchanged across time (p < 0.05). In Part II, eTL appeared longer in duration and higher in volume (PlayerLoad), but lower in intensity (Pl/min) compared to those experienced in Part I. There were no significant differences in CMJ variables across time (p < 0.05), with changes exhibiting trivial to no effect. Men experienced a significant decrease in Rate of Torque Development from Pre to Post-practice (p < 0.05), which returned to baseline at 24-hours following practice, while women experienced no changes across time. Low frequency fatigue appeared to emerge immediately following practice but resolved back to baseline at 24H-post practice. There were significant Sex differences in CMJ variables, MVC, Interpolated Twitch Torque, EMG, and twitch characteristics (p > 0.05), but no differences in percent voluntary activation. CONCLUSIONS: These findings suggest High eTL practice evoke a small acute effect on CMJ variables immediately following practice, which resolve to baseline by 24-hours, whereas Low eTL seems to induce no alteration in CMJ performance. In men, practices stimulated acute increase in testosterone and cortisol, while no changes occurred in T:C ratio. Varying eTL did not influence these acute responses in testosterone and cortisol. In women, testosterone, cortisol, and T:C ratio remained unchanged by both High and Low eTLs. Sport-specific practice appears to increase MVC and central components of neuromuscular function (voluntary activation), especially 24-hours following the exposure. Only small signs of mild peripheral fatigue occur following practice, which included low frequency fatigue appear immediately after practice, but resolved by 24-hours following the practice exposure.