EFFECT OF FATIGUE ON EXPLOSIVE STRENGTH AND MUSCLE ARCHITECTURE OF THE VASTUS LATERALIS

ABSTRACT Introduction: There has been little research on changes in rate of torque development (RTD) and muscle architecture. This study evaluated the effect of fatigue on RTD and muscle architecture of the vastus lateralis (VL). Methods: Seventeen volunteers (25.5 ± 6.2 years; 177.2 ± 12.9 cm; 76.4 ± 13.1 kg) underwent isokinetic knee extension assessment at 30°/s to obtain the peak torque (PT-ISK), before and after a set of intermittent maximal voluntary isometric contractions (MVIC) (15 reps – 3 s contraction, 3 s rest) used to promote muscle fatigue, monitored by the median frequency (MDF) of the electromyography from the VL, rectus femoris and vastus medialis muscles. Before and after the fatigue protocol, ultrasound images of the VL were obtained to measure muscle thickness (MT), fascicle length (FL), and fascicle angle (FA). The peak isometric torque (PT-ISM) and the RTDs in 50 ms windows were calculated for each MVIC. The RTDs were reported as absolute values and normalized by the PT-ISM. Results: Fatigue was confirmed due to significant reductions in MDF in all three muscles. After the fatigue protocol, the PT-ISK was reduced from 239.0±47.91 to 177.3±34.96 Nm, and the PT-MVIC was reduced from 269.5±45.63 to 220.49±46.94 Nm. All the RTD absolute values presented significant change after the fatigue protocol. However, the normalized RTD did not demonstrate any significant differences. No significant differences were found in the muscle architecture of the VL. Conclusions: The reduction in explosive strength occurred concomitantly with the reduction in maximum strength, as evidenced by the lack of changes in normalized TDT. Level of Evidence III.

Fatigue and recovery have different effects on knee biomechanics of drop vertical jump between female collegiate and recreational athletes

Background Although fatigue is known as one of the risk factors for noncontact anterior cruciate ligament injury, the effects of fatigue and recovery can be different based on the level of competition. However, it is unknown whether female recreational athletes are susceptible to fatigue or not, compared to female collegiate athletes with greater physical activity. The purpose of the present study was to examine and clarify the effects of fatigue and recovery on knee biomechanics of the drop vertical jump (DVJ) in female recreational athletes compared to female collegiate athletes. Methods Fifteen female collegiate athletes and ten female recreational athletes were enrolled in the current study. All subjects were basketball players and Tegner activity scales were level 9 and 7, respectively. They performed DVJ before and after the fatigue protocol. Three-dimensional knee kinematics and kinetics were collected during landing phase of DVJ. The data after the fatigue protocol (first, second, and third DVJs) were compared with those before the protocol using one-way repeated measures of analysis of variance in each group. Results Fatigue caused significant increase of knee abduction angle at initial contact (IC) and peak abduction moments within 40 ms from IC in female recreational athletes, whereas no increases of these parameters were observed in female collegiate athletes. Moreover, recovery from fatigue seemed to be more slowly in female recreational athletes than in female collegiate athletes as smaller knee flexion moment was observed even in post-fatigue third DVJ only for female recreational athletes. Conclusions Effects of fatigue on DVJ were significantly greater and continued for a longer duration in female recreational athletes compared to female collegiate athletes.

Possible mechanisms underlying the dynamic assembly of calcium entry units: The role of temperature and pH

Skeletal muscle function is regulated by intracellular Ca2+ levels. Two main mechanisms control movements of Ca2+ ions from intracellular stores (i.e., the sarcoplasmic reticulum; SR) and from extracellular space: (1) excitation–contraction (EC) coupling and (2) store-operated Ca2+ entry (SOCE). SOCE allows recovery of extracellular Ca2+ during prolonged muscle activity, when the SR undergoes depletion. We recently discovered that prolonged exercise leads to formation of calcium entry units (CEUs), intracellular junctions located at the I band that are formed by two distinct elements: SR stacks and transverse tubules (TTs). Assembly of CEUs during exercise promotes the interaction between STIM1 and Orai1, the two main proteins that mediate SOCE, and increases muscle resistance to fatigue in the presence of extracellular Ca2+. The molecular mechanisms underlying the exercise-dependent remodeling of SR and TT leading to CEU assembly remain to be fully elucidated. Here, we first verified whether CEUs can assemble ex vivo (in the absence of blood supply and innervation), subjecting excised EDL muscles from mice to an ex vivo incremental fatigue protocol (80 Hz tetanus stimulation lasting 45 min): the data collected demonstrate that CEUs can assemble ex vivo in isolated EDL muscles. We then evaluated if intracellular parameters that are affected by exercise, such as temperature and pH, may influence the assembly of CEUs. We found that higher temperature (36°C versus 25°C) and lower pH (7.2 versus 7.4) promotes formation of CEUs increasing the percentage of fibers containing SR stacks, the number of SR stacks/area, and the elongation of TTs at the I band. Importantly, increased assembly of CEUs at higher temperature (36°C) or at lower pH (7.2) correlated with increased fatigue resistance of EDL muscles in the presence of extracellular Ca2+, suggesting that CEUs assembled ex vivo are functional.

Alteraciones en la presión plantar posterior a un protocolo de fatiga neuromuscular en máquina isoinercial

El objetivo del presente estudio fue establecer las diferencias que se presentan en la huella plantar tras aplicar un protocolo de fatiga neuromuscular. Un total de 10 deportistas varones sanos con una edad aproximada de 21 años fueron evaluados para el componente morfológico, con el equipo Tanita BC585F® (variables: kg de peso, kg de grasa, kg de músculo y kg de hueso). En el protocolo de fatiga se utilizó el equipo isoinercial Squat RSP®. Para la prueba de baropodometría, tanto en el pre-test como en el post-test, se utilizó el equipo EcoWalk. Se tomaron variables de presión R-Type® para ambos pies, como presión media, superficie de contacto, distribución anterior, posterior, lateral derecha y lateral izquierda. No se encontraron diferencias significativas en el pre y post test de la prueba de baropodometría con una p>0.05. Se encontraron correlaciones significativas entre el componente morfológico y la baropodometría con una p<0.05. The objective of the present study sought to establish the differences presented in the plantar footprint after applying a neuromuscular fatigue protocol. A total of 10 healthy male athletes with an approximate age of 21 years were evaluated for the morphological component, with the Tanita BC585F® equipment (variables: weight Kg, fat KG, muscle Kg and bone Kg). In the fatigue protocol, the isoinertial Squat RSP® equipment was used. For the baropodometry test, both in the pre-test and in the post-test, the EcoWalk equipment was used. R-Type® pressure variables were taken for both feet, such as mean pressure, contact surface, anterior, posterior, right lateral and left lateral distribution. No significant differences were found in the pre and post test of the baropodometry test with a p> 0.05. Significant correlations were found between the morphological component and the baropodometry with a p <0.05.

Modification of Angular Kinematics and Spatiotemporal Parameters during Running after Central and Peripheral Fatigue

Fatigue causes kinematics modifications during running, and it could be related to injuries. The aim was to identify and compare the effects of central and peripheral fatigue on angular kinematics and spatiotemporal parameters during running. Angular kinematics and spatiotemporal parameters were evaluated using an infrared motion capture system and were registered during 2 min treadmill running in pre- and post-fatigue states in eighteen male recreational runners. Central fatigue was induced by a 30 min running fatigue protocol on a treadmill, while peripheral fatigue in quadriceps and hamstrings muscles was induced by an isokinetic dynamometer fatigue protocol. Central fatigue increased the anterior shank oscillation during the initial contact, knee flexion during the maximum absorption, posterior shank oscillation during propulsion, and stance time (p < 0.05). Peripheral fatigue decreased ankle dorsiflexion during initial contact and increased knee flexion and posterior shank oscillation during propulsion (p < 0.05). Moreover, central fatigue increased to a greater extent the hip and knee flexion and ankle dorsiflexion during initial contact and maximum absorption as well as stance time and propulsion time (p < 0.05). These results suggested that central fatigue causes greater increases in the range of movements during the midstance than peripheral fatigue.

Effect of Lower Extremity Fatigue on Knee Joint Kinematics During Landing Maneuvers in Adult Soccer Players

Background and Aims: Since fatigue in different regions of the lower extremities can effectively alter the movement pattern of this part of the body and cause joint-related kinematic changes that increase the risk of injury and mental fatigue, which may be a factor in reducing productivity and injury. Therefore, the study of kinematic changes during fatigue can have helpful results. This study aimed to investigate the effect of lower extremity fatigue on knee joint kinematics during landing in adult soccer players. Methods: Ten adult male soccer players (Mean±SD = age: 20.7±1.05 years; Height: 178.9±4.17 cm; Weight: 71.55±8.04 kg) participated in this study. Subjects performed a pre-test, which included jumping and landing on a 40-cm box, and recording cameras of the valgus motion analyzer, flexion, and knee rotation. The Kingtools section of the plugin software attached to the Cortex software was used for segmentation and kinematic information. The lower extremity fatigue protocol consisted of 10 repetitions of single-leg squats up to 90 degrees of knee flexion, 20 vertical jumps with a single leg, and 1 repetition of step –going up and down a 31cm step. The Borg scale was used to measure fatigue. Before and after the fatigue protocol, a single-leg hop was used to determine the level of fatigue. After the fatigue protocol, a post-test was performed. Data were analyzed using the Shapiro-Wilk test for normality of the data, and paired t-test was used to compare mean in pre-test and post-test independent variables. Results: The paired t-test results for comparison of kinematic data showed that contact flexion had a significant difference from pre-test to post-test and other kinematic variables had no significant changes from pre-test to post-test. Statistical significance was considered at P≤0.05. Conclusion: According to the findings of this study, it can be concluded that lower extremity fatigue in the present study partly caused kinematic changes in predicting ACL injury. Kinematic changes have included a decrease in Contact flexion, which is one of the predictors of ACL injury during landing.