Neuromuscular Adaptations in Endurance-Trained Male Adolescents Versus Untrained Peers: A 9-Month Longitudinal Study.

BACKGROUND: Neuromuscular function is considered as a determinant factor of endurance performance during adulthood. However, whether endurance training triggers further neuromuscular adaptations exceeding those of growth and maturation alone over the rapid adolescent growth period is yet to be determined. OBJECTIVE: The present study investigated the concurrent role of growth, maturation, and endurance training on neuromuscular function through a 9-month training period in adolescent triathletes. METHODS: Thirty-eight 13- to 15-year-old males (23 triathletes [~6 h/week endurance training] and 15 untrained [<2 h/week endurance activity]) were evaluated before and after a 9-month triathlon training season. Maximal oxygen uptake (V̇O2max) and power at V̇O2max were assessed during incremental cycling. Knee extensor maximal voluntary isometric contraction torque (MVCISO) was measured and the voluntary activation level (VAL) was determined using the twitch interpolation technique. Knee extensor doublet peak torque (T100Hz) and normalized vastus lateralis (VL) electromyographic activity (EMG/M-wave) were also determined. VL and rectus femoris (RF) muscle architecture was assessed using ultrasonography. RESULTS: Absolute V̇O2max increased similarly in both groups but power at V̇O2max only significantly increased in triathletes (+13.8%). MVCISO (+14.4%), VL (+4.4%), and RF (+15.8%) muscle thicknesses and RF pennation angle (+22.1%) increased over the 9-month period in both groups similarly (p < 0.01), although no changes were observed in T100Hz, VAL, or VL EMG/M-wave. No changes were detected in any neuromuscular variables, except for coactivation. CONCLUSION: Endurance training did not induce detectible, additional neuromuscular adaptations. However, the training-specific cycling power improvement in triathletes may reflect continued skill enhancement over the training period.

A long-duration race induces a decrease of left ventricular strains, twisting mechanics and myocardial work in trained adolescents.

We investigated the acute cardiac consequences of a long-duration (>5 h) adventure race in adolescent athletes from evaluations of left ventricular (LV) strains and myocardial work. Twenty trained male adolescents (i.e. 8 ± 4 h·week-1 of endurance sports) aged 14-17 years participated in a competitive long-duration adventure race. Blood samples were collected before, immediately and 24 h after the race to determine the time course of troponin I (cTnI) considered a myocardial damage biomarker. Resting echocardiography was conducted before and after the race to assess myocardial regional strains, LV twisting mechanics and myocardial work using speckle tracking echocardiography. The mean completion time of the race was 05:38 ± 00:20 h, with a mean heart rate (HR) of 83 ± 5% of maximal HR. cTnI concentration significantly increased in 16/20 participants after the race (pre: 0.001 ± 0.002 vs. post: 0.244 ± 0.203 ng·dL-1, p < .001) and returned to baseline within 24 h. Stroke volume, ejection fraction and global longitudinal strains remained unchanged after the race, while LV twist and global myocardial work significantly decreased (8.6 ± 3.3 vs. 6.3 ± 3.3 deg and 2080 ± 250 vs. 1781 ± 334 mmHg%, p < .05). Diastolic function, indexes of myocardial relaxation and LV untwisting rate (-91.0 ± 19.0 vs. -56.4 ± 29.1 deg·s-1, p < .001) were affected after the race. We demonstrated that in trained adolescents, a high-intensity endurance exercise of several hours induced an increase of the cTnI concentration associated with an alteration of myocardial function.HighlightsThis is the first study to explore the acute cardiac consequences of a very-long duration and high-intensity race in trained adolescentsThe cardiac evaluations before and immediately after the race were conducted using up-to-date advances in echocardiography, including not only regional left ventricular strains, rotations and twists, but also global myocardial work to consider changes in loading conditions that occur after such exercises.We observed exercise-induced cardiac fatigue in the adolescents, characterized by a drop in myocardial work, associated with an increase of cardiac troponin I in 16/20 participants.The cardiac alterations were principally observed at the apical level of the heart: the apical strains and rotations were decreased and delayed. Consequently, left ventricular twist and twisting rates were also delayed, which probably affected the diastolic function after the race.

Impact of long-duration adventure racing on hydration status, blood electrolytes and biomarkers of kidney function in trained adolescent athletes.

BACKGROUND: Little is known about the biochemical consequences of endurance activities in adolescents. The present study aimed to examine the impact of a long-duration adventure race (>5 h) on hydration status, blood electrolytes and biomarkers of kidney function in adolescent athletes. METHODS: Twenty male adolescents aged 14 to 17 y (mean±SD; body mass: 59.7±9.1 kg and maximal O2 uptake: 56.2±4.6 mL∙kg-1∙min-1) volunteered to participate in a competitive adventure race of 68.5 km. Volunteers could drink ad libitum and fluid intake was monitored throughout the race. Blood samples were collected before, within 15 minutes after, and 24 hours after the race to monitor blood electrolytes (sodium, potassium, chloride), creatinine and blood urea nitrogen (BUN). Body mass and urine specific gravity (USG) were also measured across the same time points. RESULTS: The race was completed on average in 05:38±00:20 h:min under cold and rainy conditions (10-15 °C and 83-93% of relative humidity). Fluid intake was 1.45±0.66 L and body mass decreased by 1.2% compared to before the race (P<0.001). Blood sodium concentrations remained stable after the race (140.4±2.1 mmol∙L-1) despite an expansion in the plasma volume of 8.9±15.6%. No significant variations in BUN or BUN-to-creatinine ratio occurred. A significant increase in creatinine (+13.5%, P=0.003) was observed immediately after the race but remained within the reference range. CONCLUSIONS: The long-duration race completed under cold and humid conditions seems not to have exposed adolescents to hypohydration, hyponatremia or clinically significant alterations in kidney function.

Changes in Pulmonary Function After Long-duration Adventure Racing in Adolescent Athletes.

The present study investigated the acute effects of a mixed-modality, long-duration adventure race on pulmonary function in adolescent athletes. Twenty male adolescents aged 14 to 17 years volunteered to participate in a wilderness adventure race of 68.5-km. Expiratory function was evaluated before, immediately after, and 24 h after race completion. Measurements included forced vital capacity (FVC), forced expiratory volume in 1 s (FEV1) and peak expiratory flow (PEF). Maximal inspiratory and expiratory mouth static pressures (MIP and MEP, respectively) were also measured using a portable hand-held mouth pressure meter across the same time points. The mean completion time of the race was 05:38±00:20 hours. A significant post-race decrease in FVC was observed immediately after the race (-5.2%, p=0.01). However, no significant changes were observed for FEV1, PEF and the FEV1/FVC and FEV1/PEF ratios. In addition, estimates of respiratory muscle strength (MIP and MEP) were unaffected by the race. The long-duration adventure race induced no marked reduction in expiratory pulmonary function and this response was associated with no apparent respiratory muscle fatigue. Therefore, the pulmonary system of trained adolescent athletes was sufficiently robust to sustain the mixed-modality, long-duration adventure race of ~ 5-6 h.

Neuromuscular Fatigue After Long-Duration Adventure Racing in Adolescent Athletes.

PURPOSE: To characterize the acute effects of a long-duration adventure race on knee extensor (KE) fatigue and the knee functional ratio in adolescent athletes. METHODS: Twenty trained male adolescents (aged 14-17 y) performed an adventure race of 68.5 km. Maximal voluntary isometric contraction (MVIC) KE and knee flexor torques were measured before and immediately after the race. Central and peripheral components of neuromuscular fatigue were quantified from the maximal voluntary activation level and the doublet peak torque (Tw100), respectively. The peak eccentric knee flexor torque to concentric KE torque ratio was also measured to determine functional ratio. RESULTS: The race completion time was 05:38 (00:20) hours. Significant reductions in MVICKE (-14.7%, P < .001) and MVICKF (-17.0%, P < .01) were observed after the race. Voluntary activation level decreased by 8.3% (P < .001) while Tw100 remained unchanged. Peak eccentric knee flexor torque decreased 16.0% (P < .001) while peak concentric KE torque did not change. This resulted in a significant reduction in functional ratio (-12.0%, P < .01). CONCLUSION: The adventure race induced a moderate fatigue, which was mainly explained by central factors without significant peripheral fatigue. However, particular attention should be paid to the knee muscular imbalance incurred by the race, which could increase the risk of ligament injury in adolescent athletes.

Effect of Long-Duration Adventure Races on Cardiac Damage Biomarker Release and Muscular Function in Young Athletes.

The aim of the present study was to examine the effect of 1- and 2-day adventure races on cardiac muscle damage and skeletal muscle soreness and function in young athletes. Twelve male trained adolescents (14-15 years) completed both 1-day (48.2 km) and 2-day (66.0 km) races that included trail running, mountain biking, kayaking, and in-line skating separated by 10 weeks. Myocardial damage biomarker concentrations (cTnI and CK-MB), maximal voluntary isometric contraction (MVIC) torque, perceived knee extensor (KE) muscle soreness (PMS), and drop and squat jump heights were measured before and after each race. Heart rate was also monitored throughout. Mean heart rate (% cardiac reserve) was higher during the 1-day (66.6 ± 6.4%) than 2-day (62.6 ± 7.8%, p = 0.038) race. The amplitude of cardiac damage biomarker release was also higher following the 1-day than the 2-day race (peak cTnI: 0.14 vs. 0.03 ng/mL, p = 0.045; peak CK-MB: 20.30 vs. 11.98 ng/mL, p = 0.020). However, cardiac biomarker concentrations returned to baseline at 24-48 h post-exercise, except for CK-MB after the 2-day race (p = 0.017). Eight and three participants exceeded the cTnI cut-off for myocardial injury in 1- and 2-day races, respectively, but none exceeded the cut-off for acute myocardial infarction. While there was a significant decrease in drop jump height (-5.9%, p = 0.003), MVIC torque and squat jump height remained unchanged after both races. PMS was increased at 24 h after both races (p < 0.001) but returned to baseline levels by 72 h post-race. In conclusion, the shorter, more intense race produced more cardiac damage, although this probably represents a standard exercise intensity-dependent response rather than pathological response. Skeletal muscle functional and soreness responses were moderate and similar between races.