Two-Experiment Examination of Habitual and Manipulated Foot Placement Angles on the Kinetics, Kinematics, and Muscle Forces of the Barbell Back Squat in Male Lifters.

This two-experiment study aimed to examine the effects of different habitual foot placement angles and also the effects of manipulating the foot placement angle on the kinetics, three-dimensional kinematics and muscle forces of the squat. In experiment 1, seventy lifters completed squats at 70% of their one repetition maximum using a self-preferred placement angle. They were separated based on their habitual foot angle into three groups HIGH, MEDIUM and LOW. In experiment 2, twenty lifters performed squats using the same relative mass in four different foot placement angle conditions (0°, 21°, 42° and control). Three-dimensional kinematics were measured using an eight-camera motion analysis system, ground reaction forces (GRF) using a force platform, and muscle forces using musculoskeletal modelling techniques. In experiment 1, the impulse of the medial GRF, in the descent and ascent phases, was significantly greater in the HIGH group compared to LOW, and in experiment 2 statistically greater in the 42° compared to the 21°, 0° and control conditions. Experiment 2 showed that the control condition statistically increased quadriceps muscle forces in relation to 0°, whereas the 0° condition significantly enhanced gluteus maximus, gastrocnemius and soleus forces compared to control. In experiment 1, patellofemoral joint stress was significantly greater in the HIGH group compared to LOW, and in experiment 2, patellar and patellofemoral loading were statistically greater in the control compared to the 42°, 21°, 0° and control conditions. Owing to the greater medial GRF's, increased foot placement angles may improve physical preparedness for sprint performance and rapid changes of direction. Reducing the foot angle may attenuate the biomechanical mechanisms linked to the aetiology of knee pathologies and to promote gluteus maximus, gastrocnemius and soleus muscular development. As such, though there does not appear to be an optimal foot placement angle, the observations from this study can be utilised by both strength and conditioning and sports therapy practitioners seeking to maximise training and rehabilitative adaptations.

Effect of alterations in whole-body cryotherapy (WBC) exposure on post-match recovery markers in elite Premier League soccer players.

The use of whole-body cryotherapy (WBC) as a recovery intervention is prevalent amongst elite soccer players. However, there is a distinct lack of data available around chronic WBC use and post-match recovery markers in elite soccer. The aim of this study was to investigate the impact of different levels of WBC exposure on subjective and objective measures of post-match recovery in elite soccer players during a chronic exposure period. Sixteen male senior professional outfield soccer players participated in this study over two seasons. K means cluster analysis was used to classify low (-114 ± 2°C for 133 ± 2 s), medium (-121 ± 1°C for 173 ± 2 s) and high (-133 ± 1°C for 181 ± 2 s) cryotherapy exposure indexes (CEI). Salivary markers (immunoglobulin A (IgA) and alpha amylase (AA)) and subjective wellness scores (perceived fatigue, sleep quality, general muscle soreness and stress) were collected post-match across both seasons. Training load (session-RPE) was collected and used as a covariate to control for the load amongst groups. No differences were seen in perceived measures of wellness and salivary AA. Significantly lower IgA concentrations were observed in the medium CEI group (255 ± 32 µg∙ml-1) compared to the low (328 ± 38 µg∙ml-1) and high (306 ± 32 µg∙ml-1) groups. Therefore, increasing the level of chronic WBC exposure appears to have no additional benefit on subjective recovery and alpha amylase response post-match. However, there appears to be an optimal chronic WBC dose with regards to IgA response.

A Systematic Review of Exercise Prescription in Patients with Intermittent Claudication: Does Pain Matter?

BACKGROUND: Current guidelines for intermittent claudication advocate exercise at moderate to maximal claudication pain. However, adherence rates to supervised exercise programmes (SEP) remain poor and claudication pain is a contributing factor. Limited evidence suggests that moderate or pain-free exercise may be just as beneficial and may be better tolerated. However, it remains unclear what 'level' of claudication pain is optimal for improving functional outcomes. We therefore conducted a systematic review to synthesise the evidence for exercise prescribed at different levels of claudication pain. METHODS: The CENTRAL, MEDLINE, Embase and CINAHL databases were searched up to October 2020. Randomized controlled trials (RCTs) that directly compared at least 2 different intensities of claudication pain were included. Outcome measures included walking performance, adherence, quality of life and vascular function. RESULTS: Of 1,543 search results, 2 studies were included. Maximal walking distance improved by 100-128% in the moderate-pain SEP groups, and by 77-90% in the pain-free SEP groups. Importantly, there were no significant differences between the moderate-pain and pain-free SEP groups in either study for improvements in walking performance, though comparison to a maximal-pain SEP group was not made. CONCLUSIONS: The efficacy of SEPs for patients with intermittent claudication is irrefutable, though there is no consensus on the optimal level of pain. Therefore, adequately powered RCTs are required to compare the effect of pain-free SEPs, moderate-pain SEPs and maximal-pain SEPs on functional outcomes. (PROSPERO ID: CRD42020213684).

Effect of Velocity-Based Loading on Acceleration Kinetics and Kinematics During Sled Towing.

ABSTRACT: Bentley, I, Sinclair, JK, Atkins, SJ, Metcalfe, J, and Edmundson, CJ. Effect of velocity-based loading on acceleration kinetics and kinematics during sled towing. J Strength Cond Res 35(4): 1030-1038, 2021-Sled towing (ST) provides an external load in the form of a sled towed using a shoulder or waist harness and cord behind the athlete. Loading strategies have varied greatly between studies, and despite many investigations, there is little agreement on the optimum sled loading to develop the acceleration phase. The aim of this study was to investigate the kinetics and kinematics of velocity-based ST during the acceleration phase of sprinting. Twelve academy rugby league players performed a series of 6-m sprints in different conditions; uninhibited, 10, 15, and 20% velocity decrement (VDec). Sagittal plane kinematics and kinetic measures were examined using 1-way repeated-measures analysis of variance. Results indicated that ST affected trunk, knee, and ankle joint kinematics (p < 0.05). Peak knee flexion increased as sled loads increased (p < 0.05), which may enable athletes to lower their center of mass and increase their horizontal force application. Net horizontal and propulsive impulse measures were greater in all sled conditions (p < 0.05), which increased significantly because sled loadings were heavier. In conclusion, this study highlights the effects of differential loads to help coaches understand acute kinetics and kinematic changes to improve the planning of sprint training.

Sex differences in ACL loading and strain during typical athletic movements: a musculoskeletal simulation analysis.

PURPOSE: Female athletes experience anterior cruciate ligament (ACL) injuries at a much greater rate than males, yet the mechanisms responsible for this are not well-understood. The current investigation aimed using a musculoskeletal simulation-based approach, to examine sex differences in ACL loading parameters during cut and hop movements. METHODS: Fifteen male and fifteen female participants completed 45° cut and maximal one legged hop movements. Three-dimensional motion capture and ground reaction force data during the stance phase of the cut movement and landing phase of the one legged hop were obtained. Lower extremity muscle forces, ACL forces and ACL strains were extracted via a simulation-based approach using a musculoskeletal model, with an ACL insertion into the femur and tibia. RESULTS: During the hop movement, females were associated with significantly greater peak ACL forces (male = 15.01 N/kg and female = 15.70 N/kg) and strains (male = 6.87% and female = 10.74%). In addition, for both the cut (male = 4.45 and female = 1.45) and hop (male = 2.04 and female = 1.46) movements, the soleus/gastrocnemius ratio was significantly larger in males. CONCLUSIONS: The current investigation provides new information regarding sex differences during athletic movements that provide further insight regarding the increased incidence of ACL injuries in females.

Effects of a Prophylactic Knee Sleeve on Anterior Cruciate Ligament Loading During Sport-Specific Movements.

CONTEXT: Prophylactic knee bracing is extensively utilized in athletic populations to reduce the high risk from knee injuries, but its role in the attenuation of anterior cruciate ligament (ACL) pathologies is not well understood. OBJECTIVE: The aim of this investigation was to explore the effects of a prophylactic knee sleeve on ACL loading parameters linked to the etiology of injury in recreational athletes. SETTING: Laboratory. DESIGN: Repeated measures. PARTICIPANTS: Thirteen healthy male recreational athletes. INTERVENTION: Participants performed run, cut, and single-leg hop movements under 2 conditions; prophylactic knee sleeve and no sleeve. MAIN OUTCOME MEASURES: Biomechanical data were captured using an 8-camera 3D motion capture system and a force platform. Peak ACL force, average ACL load rate, and instantaneous ACL load rate were quantified using a musculoskeletal modeling approach. RESULTS: The results showed that both average and instantaneous ACL load rates were significantly reduced when wearing the knee sleeve in the hop (sleeve = 612.45/1286.39 N/kg/s and no sleeve = 743.91/1471.42 N/kg/s) and cut (sleeve = 222.55/1058.02 N/kg/s and no sleeve = 377.38/1183.01 N/kg/s) movements. CONCLUSIONS: Given the biomechanical association between ACL loading and the etiology of ACL injuries, it is proposed that athletes may be able to attenuate their risk from injury during cut and hop movements through utilization of a prophylactic knee sleeve.

Influence of wheel size on muscle activity and tri-axial accelerations during cross-country mountain biking.

This study aimed to investigate the influence of different mountain bike wheel diameters on muscle activity and whether larger diameter wheels attenuate muscle vibrations during cross-country riding. Nine male competitive mountain bikers (age 34.7 ± 10.7 years; stature 177.7 ± 5.6 cm; body mass 73.2 ± 8.6 kg) participated in the study. Riders performed one lap at race pace on 26, 27.5 and 29 inch wheeled mountain bikes. sEMG and acceleration (RMS) were recorded for the full lap and during ascent and descent phases at the gastrocnemius, vastus lateralis, biceps brachii and triceps brachii. No significant main effects were found by wheel size for each of the four muscle groups for sEMG or acceleration during the full lap and for ascent and descent (P > .05). When data were analysed between muscle groups, significant differences were found between biceps brachii and triceps brachii (P < .05) for all wheel sizes and all phases of the lap with the exception of for the 26 inch wheel during the descent. Findings suggest wheel diameter has no influence on muscle activity and vibration during mountain biking. However, more activity was observed in the biceps brachii during 26 inch wheel descending. This is possibly due to an increased need to manoeuvre the front wheel over obstacles.

The effect of mountain bike wheel size on cross-country performance.

The purpose of this study was to determine the influence of different wheel size diameters on indicators of cross-country mountain bike time trial performance. Nine competitive male mountain bikers (age 34.7 ± 10.7 years; stature 177.7 ± 5.6 cm; body mass 73.2 ± 8.6 kg) performed 1 lap of a 3.48 km mountain bike (MTB) course as fast as possible on 26″, 27.5″ and 29″ wheeled MTB. Time (s), mean power (W), cadence (revs · min-1) and velocity (km · h-1) were recorded for the whole lap and during ascent and descent sections. One-way repeated measure ANOVA was used to determine significant differences. Results revealed no significant main effects for any variables by wheel size during all trials, with the exception of cadence during the descent (F(2, 16) = 8.96; P = .002; P2 = .53). Post hoc comparisons revealed differences lay between the 26″ and 29″ wheels (P = .02). The findings indicate that wheel size does not significantly influence performance during cross-country when ridden by trained mountain bikers, and that wheel choice is likely due to personal choice or sponsorship commitments.

Impact of Harness Attachment Point on Kinetics and Kinematics During Sled Towing.

Resisted sprint training is performed in a horizontal direction and involves similar muscles, velocities, and ranges of motion (ROM) to those of normal sprinting. Generally, sleds are attached to the athletes through a lead (3 m) and harness; the most common attachment points are the shoulder or waist. At present, it is not known how the different harness point's impact on the kinematics and kinetics associated with sled towing (ST). The aim of the current investigation was to examine the kinetics and kinematics of shoulder and waist harness attachment points in relation to the acceleration phase of ST. Fourteen trained men completed normal and ST trials, loaded at 10% reduction of sprint velocity. Sagittal plane kinematics from the trunk, hip, knee, and ankle were measured, together with stance phase kinetics (third footstrike). Kinetic and kinematic parameters were compared between harness attachments using one-way repeated-measures analysis of variance. The results indicated that various kinetic differences were present between the normal and ST conditions. Significantly greater net horizontal mean force, net horizontal impulses, propulsive mean force, and propulsive impulses were measured (p < 0.05). Interestingly, the waist harness also led to greater net horizontal impulse when compared with the shoulder attachment (p < 0.001). In kinematic terms, ST conditions significantly increased peak flexion in hip, knee, and ankle joints compared with the normal trials (p < 0.05). Results highlighted that the shoulder harness had a greater impact on trunk and knee joint kinematics when compared with the waist harness (p < 0.05). In summary, waist harnesses seem to be the most suitable attachment point for the acceleration phase of sprinting. Sled towing with these attachments resulted in fewer kinematic alterations and greater net horizontal impulse when compared with the shoulder harness. Future research is necessary in order to explore the long-term adaptations of these acute changes.

The Presence of Bilateral Imbalance of the Lower Limbs in Elite Youth Soccer Players of Different Ages.

The aim of this study was to examine bilateral differences in ground reaction forces (GRF), measured during a deep squat (DS) exercise, in a population of elite youth soccer players. Bilateral muscle balance is a key component in promoting musculoskeletal health of performers, yet there is a limited evidence base investigating such imbalances in youth. Seventy-four subjects were assigned to performance groups according to chronological age (younger than 13, 14, 15, 16, 17 years). Analysis of physical maturity status revealed that very few players were classified as "early" or "late" maturers. Players completed an overhead DS exercise, as part of preseason functional movement screening. Peak GRF were assessed using a twin force plate system. Significant differences (p ≤ 0.05) were identified between right and left side peak GRF for all groups except the youngest (U13) and oldest (U17). Nondominant "sides" showed the highest levels of PGRF across all groups. The magnitude of PGRF was not significantly different both within and between groups, except for the left side in the U13 to U15 groups (p = 0.04). Results from this study show that performance asymmetry is marked in adolescence. There seems a "trigger point" during the early stage of adolescence, when bilateral imbalances become marked. These differences do seem to reduce during the later stages of adolescence. Correct attention to focussed training, designed to remediate any imbalance, is warranted in adolescent groups. This is important with respect of the key associations between bilateral asymmetry and risk of injury.

The Influence of Minimalist and Maximalist Footwear on Patellofemoral Kinetics During Running.

The current study aimed to comparatively examine the effects of minimalist, maximalist, and conventional footwear on the loads experienced by the patellofemoral joint during running. Twenty male participants ran over a force platform at 4.0 m×s-1. Lower limb kinematics were collected using an 8-camera motion capture system allowing patellofemoral kinetics to be quantified using a musculoskeletal modeling approach. Differences in patellofemoral kinetic parameters were examined using one-way repeated-measures ANOVA. The results showed the peak patellofemoral force and pressure were significantly larger in conventional (4.70 ± 0.91 BW, 13.34 ± 2.43 MPa) and maximalist (4.74 ± 0.88 BW, 13.59 ± 2.63 MPa) compared with minimalist footwear (3.87 ± 1.00 BW, 11.59 ± 2.63 MPa). It was also revealed that patellofemoral force per mile was significantly larger in conventional (246.81 ± 53.21 BW) and maximalist (251.94 ± 59.17 BW) as compared with minimalist (227.77 ± 58.60 BW) footwear. As excessive loading of the patellofemoral joint has been associated with the etiology of patellofemoral pain symptoms, the current investigation indicates that minimalist footwear may be able reduce runners' susceptibility to patellofemoral disorders.

Electromyographic response of global abdominal stabilizers in response to stable- and unstable-base isometric exercise.

Core stability training traditionally uses stable-base techniques. Less is known as to the use of unstable-base techniques, such as suspension training, to activate core musculature. This study sought to assess the neuromuscular activation of global core stabilizers when using suspension training techniques, compared with more traditional forms of isometric exercise. Eighteen elite level, male youth swimmers (age, 15.5 ± 2.3 years; stature, 163.3 ± 12.7 cm; body mass, 62.2 ± 11.9 kg) participated in this study. Surface electromyography (sEMG) was used to determine the rate of muscle contraction in postural musculature, associated with core stability and torso bracing (rectus abdominus [RA], external obliques [EO], erector spinae [ES]). A maximal voluntary contraction test was used to determine peak amplitude for all muscles. Static bracing of the core was achieved using a modified "plank" position, with and without a Swiss ball, and held for 30 seconds. A mechanically similar "plank" was then held using suspension straps. Analysis of sEMG revealed that suspension produced higher peak amplitude in the RA than using a prone or Swiss ball "plank" (p = 0.04). This difference was not replicated in either the EO or ES musculature. We conclude that suspension training noticeably improves engagement of anterior core musculature when compared with both lateral and posterior muscles. Further research is required to determine how best to activate both posterior and lateral musculature when using all forms of core stability training.

The effects of orthotic intervention on multisegment foot kinematics and plantar fascia strain in recreational runners.

Chronic injuries are a common complaint in recreational runners. Foot orthoses have been shown to be effective for the treatment of running injuries but their mechanical effects are still not well understood. This study aims to examine the influence of orthotic intervention on multisegment foot kinematics and plantar fascia strain during running. Fifteen male participants ran at 4.0 m · s(-1) with and without orthotics. Multisegment foot kinematics and plantar fascia strain were obtained during the stance phase and contrasted using paired t tests. Relative coronal plane range of motion of the midfoot relative to the rearfoot was significantly reduced with orthotics (1.0°) compared to without (2.2°). Similarly, relative transverse plane range of motion was significantly lower with orthotics (1.1°) compared to without (1.8°). Plantar fascia strain did not differ significantly between orthotic (7.1) and nonorthotic (7.1) conditions. This study shows that although orthotics did not serve to reduce plantar fascia strain, they are able to mediate reductions in coronal and transverse plane rotations of the midfoot.

The test-retest reliability of knee joint center location techniques.

The principal source of measurement error in three-dimensional analyses is the definition of the joint center about which segmental rotations occur. The hip joint has received considerable attention in three-dimensional modeling analyses yet the reliability of the different techniques for the definition of the knee joint center has yet to be established. This study investigated the reliability of five different knee joint center estimation techniques: femoral epicondyle, femoral condyle, tibial ridge, plugin- gait, and functional. Twelve male participants walked at 1.25 m·s-1 and three-dimensional kinetics/kinematics of the knee and ankle were collected. The knee joint center was defined twice using each technique (test-and-retest) and the joint kinetic/kinematic data were applied to both. Wilcoxon rank tests and intraclass correlation coefficients (ICCs) were used to compare test and retest angular parameters and kinematic waveforms. The results show significant differences in coronal and transverse planes angulation using the tibial ridge, plug-in-gait, and functional methods. The strongest test-retest ICCs were observed for the femoral epicondyle and femoral condyle configurations. The findings from the current investigation advocate that the femoral epicondyle and femoral condyle techniques for the estimation of the knee joint center are currently the most reliable techniques.

Influence of running shoes and cross-trainers on Achilles tendon forces during running compared with military boots.

Military recruits are known to be susceptible to Achilles tendon pathology. The British Army have introduced footwear models, the PT-03 (cross-trainer) and PT1000 (running shoes), in an attempt to reduce the incidence of injuries. The aim of the current investigation was to examine the Achilles tendon forces of the cross-trainer and running shoe in relation to conventional army boots. Ten male participants ran at 4.0 m/s in each footwear condition. Achilles tendon forces were obtained throughout the stance phase of running and compared using repeated-measures ANOVAs. The results showed that the time to peak Achilles tendon force was significantly shorter when running in conventional army boots (0.12 s) in comparison with the cross-trainer (0.13 s) and running shoe (0.13 s). Achilles tendon loading rate was shown to be significantly greater in conventional army boots (38.73 BW/s) in comparison with the cross-trainer (35.14 BW/s) and running shoe (33.57 BW/s). The results of this study suggest that the running shoes and cross-trainer footwear are associated with reductions in Achilles tendon parameters that have been linked to the aetiology of injury, and thus it can be hypothesised that these footwear could be beneficial for military recruits undertaking running exercises.

Influence of new military athletic footwear on the kinetics and kinematics of running in relation to army boots.

Musculoskeletal injuries in the lower extremities are common in military recruits. Army boots have frequently been cited as a potential mechanism behind these high injury rates. In response to this, the British Army introduced new footwear models, the PT-03 (cross-trainer) and PT1000 (running shoes), which are issued to each new recruit in an attempt to reduce the incidence of these injuries. The aim of the current investigation was to examine the kinetics and kinematic of the PT-03 and PT1000 footwear in relation to conventional army boots. Thirteen participants ran at 4.0 m·s in each footwear condition. Three-dimensional kinematics from the hip, knee, and ankle were measured using an 8-camera motion analysis system. In addition, simultaneous ground reaction forces were obtained. Kinetic parameters were obtained alongside joint kinematics and compared using repeated-measures analyses of variance. The kinetic analysis revealed that impact parameters were significantly greater when running in the army boot compared with the PT-03 and PT1000. The kinematic analysis indicated that, in comparison with the PT-03 and PT1000, running in army boots was associated with significantly greater eversion and tibial internal rotation. It was also found that when running in the PT-03 footwear, participants exhibited significantly greater hip adduction and knee abduction compared with the army boots and PT1000. The results of this study suggest that the army boots and PT-03 footwear are associated with kinetic and kinematic parameters that have been linked to the etiology of injury; thus, it is recommended that the PT1000 footwear be adopted for running exercises.

The influence of different force and pressure measuring transducers on lower extremity kinematics measured during running.

In running analyses where both kinetic and kinematic information is recorded, participants are required to make foot contact with a force and/or pressure measuring transducer. Problems arise if participants modify their gait patterns to ensure contact with the device. There is currently a paucity of research investigating the influence of different underfoot kinetic measuring devices on 3-dimensional kinematics of running. Fifteen participants ran at 4.0 m/s in four different conditions: over a floor embedded force plate, Footscan, Matscan, and with no device. Three-dimensional angular kinematic parameters were collected using an eight camera motion analysis system. Hip, knee, and ankle joint kinematics were contrasted using repeated-measures ANOVAs. Participants also rated their subjective comfort in striking each of the three force measuring devices. Significant differences from the uninhibited condition were observed using the Footscan and Matscan in all three planes of rotation, whereas participants subjectively rated the force plate significantly more comfortable than either the Footscan/Matscan devices. The findings of the current investigation therefore suggest that the disguised floor embedded force plate offers the most natural running condition. It is recommended that analyses using devices such as the Footscan/Matscan mats overlying the laboratory surface during running should be interpreted with caution.

Perceptions, behaviours and barriers towards exercise practices in inflammatory bowel disease.

Inflammatory bowel disease (IBD), a chronic disease affecting the digestive tract, has a significant impact on health-related quality of life. Pharmaceutical treatment is typically adopted, yet exercise is increasingly becoming recognized as an adjunct therapy. This study aimed to explore the perspectives, behaviours, and barriers of IBD patients in terms of their exercise habits. A 16-item closed-ended questionnaire was completed by 463 adult IBD patients (Ulcerative colitis = 57.02%, Crohn's dis-ease = 40.60% and Other = 2.38%) (Female = 76.67%, Male = 22.46 and Non-binary = 0.86%). The questionnaire was divided into three sections: baseline/demographic characteristics, disease characteristics, and exercise perceptions, beliefs, and behaviours. Significantly (P<0.001) more participants (63.07%) reported that they engage regularly with exercise compared to those who do not; however, engagement was significantly lower in female patients (59.72%) compared to males (74.04%). Respondents also rated significantly (P<0.001) that a combination of factors prevents engagement in exercise (74.30%). Moderate intensity exercise was the predominant (P<0.001) aerobic modality (39.04%), the majority (P<0.001) response was that patients undertake no resistance training (27.74%), and significantly more (P<0.001) patients indicated that they don't know whether resistance training can influence IBD either positively (57.53%) or negatively (62.33%). Whilst it is encouraging that IBD patients are engaging regularly with exercise, the reduced levels of engagement in females and lack of knowledge/ engagement with resistance training, indicate that future implementation and educational developments are necessary to enhance exercise in females and resistance training engagement in all IBD patients.