An anterior cruciate ligament (ACL) injury is one of the most common severe knee injuries in sports. The purpose of this review was to summarize the studies that directly quantified in vivo ACL loading as a function of knee motion in healthy individuals during static, slow-speed and athletic tasks.
A systematic review of the literature in multiple databases was conducted using different combinations of the terms “anterior cruciate ligament” or “ACL” and “in vivo” combined with “tensile” “strain” “stress” “force” and “loading”.
A total of 27 studies were identified. Eleven studies utilized strain sensors, while 16 studies applied imaging techniques. The numbers of studies for static or semi-static postures, slow-speed tasks, and athletic tasks were 12, 11 and 4, respectively.
There were strong and negative correlations between ACL elongation and knee flexion angles across different tasks. Peak ACL elongation mostly occurred when the knee flexion angle was minimal. Increased tibial anterior shear forces and patellar tendon forces would increase ACL loading when the knee is kept at a constantly small angle. In addition, a high patellar tendon force could be generated by preparatory quadriceps activation to load the ACL even when the lower extremity was not in contact with the ground during athletic tasks. Furthermore, while exercise modalities might affect peak ACL loading, the relationship between exercise intensities and ACL loading was complex and should not be assumed to be linear.
The purpose of this investigation was to examine the acute effects of low-load unilateral submaximal leg extension muscle actions with and without blood flow restriction (BFR) on maximal voluntary isometric contraction (MVIC) torque, electromyographic (EMG) amplitude (AMP) and EMG mean power frequency (MPF).
Twelve (mean ± SD; 23 ± 4 years) men performed 75 submaximal (1 × 30, 3 × 15) unilateral leg extension muscle actions with or without BFR. Before and immediately after the 75 reps, ultrasound measures and MVIC muscle actions were performed, and surface EMG was simultaneously assessed from the vastus lateralis. BFR was applied at 60% of total arterial occlusion. Separate repeated measures ANOVA’s, and Bonferroni corrected t-tests were performed to examine MVIC, EMG AMP, and EMG MPF. An alpha of P < 0.05 was considered statistically significant for all comparisons.
There was no significant (P = 0.077) interaction or main effect for Condition (P = 0.442) for EMG AMP. There was, however, an interaction (P = 0.014) for EMG MPF (posttest BFR decrease > posttest non-BFR decrease). There was a main effect for Time, collapsed across Condition, for MVIC torque (P < 0.001; (mean ± SD; 294.9 ± 20.1 N·m to 138.6 ± 12.2 N·m), but no main effect for Time for EMG AMP.
The findings of the present study indicated there were similar fatigue-induced decreases in MVIC torque and mode-specific decreases in EMG mean power frequency between the BFR and non-BFR conditions, but no changes in EMG amplitude. The decrease in MVIC torque may be due, in part, to the fatigue-induced buildup of metabolic byproducts that adversely affects excitation–contraction coupling and force output.
The purpose of this study was to examine the responses of electromyographic (EMG) and mechanomyographic (MMG) amplitude across the torque spectrum in pre- and post-pubescent males and females.
Forty pre-pubescent (mean ± 95% confidence interval, age = 9.79 ± 0.35 years, n = 10 males, n = 10 females) and post-pubescent (age = 17.23 ± 0.58 years, n = 10 males, n = 10 females) participants completed this study. Participants completed maximal voluntary isometric contractions (MVICs) of the forearm flexors and extensors, as well as isometric ramp muscle actions. EMG and MMG amplitude were quantified from the biceps brachii, brachialis, and brachioradialis during all muscle actions. EMG and MMG amplitude during the isometric ramp muscle actions were normalized to EMG and MMG amplitude from the MVICs.
The pre-pubertal group tended to have greater relative EMG amplitude across intensity (P < 0.050), while the post-pubertal group had a more pronounced increase in EMG amplitude at higher intensities. Similarly, the pre-pubertal group tended to have greater relative MMG amplitude across intensity (P ≤ 0.004) that plateaued earlier than the post-pubertal group (55% vs. 65%–75% of MVIC). Additionally, the pre-pubertal group had greater coactivation across intensity (P ≤ 0.001).
The greater relative EMG and MMG amplitude in the pre-pubertal group, in conjunction with the earlier plateau in MMG amplitude for the pre-pubertal group and greater coactivation, suggests less efficient muscle activation and motor unit recruitment strategies during pre-pubescence. Taken together, the findings of the present study suggest that growth-mediated changes in neuromuscular function lead to improvements in the efficiency of muscular activation and augmentations in motor unit recruitment strategies.
To assess the acute effect of moderate and high-intensity exercise on markers of cardio-metabolic function among rotational shift workers.
Sedentary men (n = 26, age: 38 ± 8 years; BMI: 32.2 ± 6.0 kg/m2, VO2peak 32.6 ± 6.7 mL/kg/min) employed in rotational shift work were recruited and underwent objectively assessed sleep quality (~ 7 days actigraphy) prior to reporting for laboratory testing. Baseline venous blood was collected to analyse fasted glucose, insulin and inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-1 receptor antagonist (IL-1Ra). Participants were randomly allocated a 30 min cycling intervention of either high intensity interval training (HIIT): 1:4 ratio of 60 s at 100% and 240 s at 50% VO2peak, or moderate intensity continuous training (MICT); continuous cycling at 60% VO2peak. Fasted venous blood was collected post intervention (0, 30, 60 min) before subsequent night’s sleep was assessed via actigraphy.
HIIT (P < 0.016) and MICT (P < 0.016) significantly increased IL-1Ra immediately and 30 min post exercise. Significantly decreased wake after sleep onset (WASO) were observed following MICT (P < 0.05). No significant changes were observed for supplementary sleep variables, insulin sensitivity, IL-6 or TNF-α for either intervention group (P > 0.05).
High- and moderate-intensity exercise acutely increase anti-inflammatory markers post exercise and MICT significantly reduces sleep fragmentation in rotational shift workers. Results which are associated with improved cardio-metabolic function and indicate the potential validity of exercise as an intervention to offset the hypothesised adverse health effects of rotational shift work.
High-intensity exercise reduces renal artery blood flow (RBF) compared to other forms of exercise. However, it is unclear whether moderate-intensity exercise, including those at the ventilation threshold (VT), decreases RBF. Additionally, attenuated renal autoregulation and associated blood flow can cause renal injury in patients with underlying disease. Therefore, this study aimed to confirm the changes in RBF after moderate-level exercise in healthy subjects, which will have implications for the study of renal arterial blood flow in patients with renal failure.
Cardiopulmonary exercise tests were performed by 10 healthy male participants (mean age, 31 ± 8 years): 3 min constant work-rate exercise tests, varying in exercise intensity 1 min before VT (pre-VT), after VT (post-VT), and after the respiratory compensation point (RCP). The RBF was measured using ultrasonic inspection equipment following each exercise. The VT was determined using the ventilatory equivalent method (VEQ method), while the RBF was calculated from the time-averaged flow velocity (TAV) and cross-sectional area (CSA).
At baseline (resting phase), RBF was 461 ± 142 mL/min. While RBFs at pre-VT were not significantly different from those at baseline (482 ± 142 mL/min; P = 0.82), significant differences were observed at post-VT (289 ± 111 mL/min; P < 0.01 vs. baseline). RBFs at the RCP were also different from those at the baseline (212 ± 56 mL/min; P < 0.01 vs. baseline).
In healthy individuals, exercises varying in intensity up to the vicinity of the VT can be performed without any significant decrease in RBF.
The trial was approved by an independent ethics committee at the Asahi University Hospital (approval No. 1/May/2018) and was registered (Name of the registry: Changes of renal blood flow with exercise load. Consideration using ultrasonic inspection equipment. UMIN000035598, https://center6.umin.ac.jp/cgi-open-bin/ctr/ctr_view.cgi?recptno=R000040561, 24/January/2019).
Kubios is an intuitive software intended to provide heart rate variability (HRV) processing. It is widely used to assess athletes’ readiness for new training sessions and autonomic balance responses to the training programme. However, Kubios’ filtering levels’ effect on artefact correction for elite athletes is still unclear. This study aims to assess the impact of different Kubios threshold-based artefact correction levels on the HRV-derived parameters in male and female elite athletes.
One hundred and seventeen elite athletes (55 females) from 21 Olympic sports participated in this study. All participants underwent an HRV recording in the morning after 24 h of no intense exercise, caffeine, and alcohol consumption. The heart rate signals were acquired with the Polar V800 monitor, and time and frequency domain-derived variables were calculated with and without Kubios’ five levels of filtering.
Kubios filtering levels significantly affected the HRV results in both time and frequency domains in female and male elite athletes. “Medium”, “Strong”, and “Very Strong” filtering resulted in an interpolation larger than 5% (above recommended by the software developers) in 3.4%, 28.2%, and 95% of the entire group data, respectively. Moreover, the “Very Strong” filter significantly lowered HRV variables and promoted mean values exceeding the 5% interpolation for females (33.35%) and males (38.17%).
The “Very Low” and “Low” threshold-based artefact correction levels were more suitable for processing HRV data from female and male elite athletes when Kubios was used.
Special tactical units differ from other police departments, for having more physically demanding tasks and occupations. Therefore, the aim was to analyze: (i) the differences in anthropometrics, body composition, and physical performance variables between those officers with the highest and lowest lean mass (LM) and fat mass (FM); and (ii) the associations between body composition (i.e., FM and LM) and some selected performance variables.
Thirty-six special operations officers (n = 36, age: 35.97 ± 5.50 years) volunteered to participate in this study. Participants were assessed for anthropometrics and body composition through skin-fold measures. Additionally, fitness was evaluated using appropriate physical tests (i.e. 30-m sprints, vertical jump, strength and endurance). Afterwards, participants were divided according to their level of LM and FM into: high (LMhigh and FMhigh) and low (LMlow and FMlow).
Regarding strength and jump performance, LMhigh and FMlow obtained better estimated values in Squat (1 repetition maximum [SQ1RM]), and jump height (P < 0.05; ES = 0.62–1.29), although non-significant but small differences were observed for relative strength (P = 0.107; ES = 0.54). In terms of sprint and endurance, the results indicated that LMhigh and FMlow obtained significantly better performances across all measures (P < 0.05; ES > 0.89), except for endurance between FMhigh and FMlow (ES = 0.25–0.65). In addition, FM and LM were significantly associated with physical performance (P < 0.05; r > 0.383) in most of the variables of this study.
Higher LM and lower FM are determinant factors of physical performance in this population. Moreover, FM and LM seemed to be detrimental for physical performance as shown by the moderate to large correlations observed.
The present study engaged in an ethnographical observation of the processes used to determine player (de)selections within a professional academy. English category-2 youth academy players (n = 96) from U10–U16 age groups undertook anthropometric profiling (height, mass and somatic maturation) and fitness assessments (10 m, 20 m & 30 m linear sprints, 505-agility test, countermovement and squat jumps). Each players lead coach (n = 4) subjectively graded players utilising a red, amber and green (RAG) rating system on a weekly (current performance) and quarterly (perceived potential) basis, across 25 weeks. A MANCOVA, controlling for maturation, was applied to determine differences in (de)selection by physical performance. Mann Whitney-U tests were used to distinguish difference in (de)selection by subjective grading (weekly and quarterly). The key finding was that quarterly subjective gradings established a higher cumulative score of green ratings in selected players and a low cumulative score of red ratings, and vice versa for deselected players (P ≤ 0.001 to 0.03). However, whilst these findings suggest that quarterly subjective grades of potential were able to provide the best predictors for player (de)selection, the findings should be viewed with caution due to high potential for confirmatory bias.
Rate of force development (RFD) and impulse (IMP) are important mechanical measures of muscular performance but are relatively unused within the rehabilitation and performance community. Due principally to access to low-cost testing devices and understanding the utility of these measures. The aim of this study therefore was to quantify the reliability of various force–time variables using load-cell technology collected via isometric knee extension whilst constrained in an isokinetic device (CON90) or unconstrained on a physiotherapy plinth at 60 and 90 degree angles (UNCON60 and UNCON90). Thirty-two volunteers had their peak force (PF), RFD, peak RFD (PRFD), and IMP assessed across three protocols. For all variables, UNCON60 had the largest variability across all measures. PF and PRFD were found to have small variability (ICC > 0.67 and CV < 10%). With regards to RFD 2080 all three protocols were found to have moderate variability all ICCs above 0.75, however, all CVs were greater than 10% ranging from ~ 11%–22%. Finally, IMP 2080 was found to have moderate variability for both CON90 and UNCON90, the absolute consistency once more greater than 10% (~ 11%–25%). Using the constrained and unconstrained protocols, PF and PRFD can be measured reliably between trials with 90 degree knee position.
Dietary analysis is an important part of the sports nutrition practitioners’ role, however the ability to accurately collect and analyze dietary intake data is questionable. The remote food photography method (RFPM) has been proposed as a low-burden and potentially valid approach to collecting and interpreting dietary intake data. Preliminary research suggests that this is valid in some athletic populations, however the ecological validation in real-life settings warrants further investigation.
Twenty athletic individuals completed simultaneous three-day RFPM diaries and weighed food diaries for the analysis of energy, protein, carbohydrate, and fat. Participants were required to provide details alongside provided photographs that did not include food weights to allow for the estimation of nutrient intake from minimally invasive photographs and descriptions.
RFPM demonstrated non-significant random and systematic error against the weighed food diary for energy, protein, carbohydrate, and fat at − 20.0 ± 455.5 kcal, − 2.9 ± 34.6 g, − 12.4 ± 49.3 g and 2.3 ± 26.8 g, respectively. Coefficient of variation suggest acceptable agreement between RFPM and weighed food diary for energy and poor agreement for protein, carbohydrate, and fat. Considerable variability is observed in the individual calculated values, with the least and greatest difference being 0% and − 83.0%, respectively.
The results indicate that the RFPM may be an ecologically valid tool for the collection and analysis of dietary intake data on a group level; on an individual basis, data and subsequent recommendations based on this method must be applied with caution.