Kinematic and EMG activities during front and back squat variations in maximum loads.

The aim of this study was to compare the musculature activity and kinematics of knee and hip joints during front and back squat with maximal loading. Two-dimensional kinematical data were collected and electromyographic activities of vastus lateralis, vastus medialis, rectus femoris, semitendinosus, biceps femoris, gluteus maximus and erector spinae were measured while participants (n = 12, 21.2 ± 1.9 years old) were completing front and back squat exercises with maximum loading. Paired sample t-test was used for comparisons between two techniques. Results showed that the electromyographic activity of vastus medialis was found to be greater in the front squat compared to the back squat during the ascending phase (P < 0.05, d = 0.62; 95% CI, -15.0/-4.17) and the whole manoeuvre (P < 0.05, d = 0.41; 95% CI, -12.8/-0.43), while semitendinosus (P < 0.05, d = -0.79; 95% CI, 0.62/20.59) electromyographic activity was greater in the back squat during the ascending phase. Compared to the front squat version, back squat exhibited significantly greater trunk lean, with no differences occurring in the knee joint kinematics throughout the movement. Results may suggest that the front squat may be preferred to the back squat for knee extensor development and for preventing possible lumbar injuries during maximum loading.

Effect of Knee Hyperextension on Femoral Cartilage Thickness in Stroke Patients.

OBJECTIVE: Knee hyperextension is one of the most common compensatory mechanisms in stroke patients. The first aim of the study was to measure knee hyperextension and femoral cartilage thickness in stroke patients. The second aim was to compare the femoral cartilage thickness of the paretic and nonparetic limbs in stroke patients with and without knee hyperextension. DESIGN: Forty stroke patients were included in the study. The patients were divided into two groups according to the presence of knee hyperextension based on kinematic analyses performed during walking with a three-dimensional motion analysis system. The medial femoral cartilage, lateral femoral cartilage, and intercondylar cartilage thicknesses of the paretic and nonparetic sides of the patients were measured by ultrasonography. RESULTS: In the study group, medial femoral cartilage, intercondylar, and lateral femoral cartilage thicknesses were less on the paretic side than on the nonparetic side, while the femoral cartilage thicknesses on the paretic and nonparetic sides were similar in the control group. Paretic side medial femoral cartilage and intercondylar thicknesses were less in the study group compared with the control group, and lateral femoral cartilage thickness was similar between the two groups. CONCLUSIONS: Knee hyperextension during walking causes femoral cartilage degeneration in stroke patients.Clinical Trial code: NCT05513157.

Effect of hold depth and grip technique on maximal finger forces in rock climbing.

The aim of this study was to understand how the commonly used climbing-specific grip techniques and hold depths influence the finger force capacities. Ten advanced climbers performed maximal voluntary force on four different hold depths (from 1 to 4 cm) and in two force directions (antero-posterior and vertical) using three grip techniques (slope, half crimp and full crimp). A specially designed platform instrumented with a 6-degrees-of-freedom (DoF) force/torque sensor was used to record force values. Results showed that the maximal vertical forces differed significantly according to the hold depth and the grip technique (ranged from 350.8 N to 575.7 N). The maximal vertical forces increased according to the hold depth but the form of this increase differed depending on grip technique. These results seemed to be more associated with finger-hold contact/interaction than with internal biomechanical factors. Similar results were revealed for antero-posterior forces (ranged from 69.9 N to 138.0 N) but, it was additionally noted that climbers have different hand-forearm posture strategies with slope and crimp grip techniques when applying antero-posterior forces. This point is important as it could influence the body position adopted during climbing according to the chosen grip technique. For trainers and designers, a polynomial regression model was proposed in order to predict the mean maximal force based on hold depth and adopted grip technique.

The effect of chalk on the finger-hold friction coefficient in rock climbing.

The main purpose of this study was to examine the effect of chalk on the friction coefficient between climber's fingers and two different rock types (sandstone and limestone). The secondary purpose was to investigate the effects of humidity and temperature on the friction coefficient and on the influence of chalk. Eleven experienced climbers took part in this study and 42 test sessions were performed. Participants hung from holds which were fixed on a specially designed hang board. The inclination of the hang board was progressively increased until the climber's hand slipped from the holds. The angle of the hang board was simultaneously recorded by using a gyroscopic sensor and the friction coefficient was calculated at the moment of slip. The results showed that there was a significant positive effect of chalk on the coefficient of friction (+18.7% on limestone and +21.6% on sandstone). Moreover sandstone had a higher coefficient of friction than limestone (+15.6% without chalk, +18.4% with chalk). These results confirmed climbers' belief that chalk enhances friction. However, no correlation with humidity/temperature and friction coefficient was noted which suggested that additional parameters should be considered in order to understand the effects of climate on finger friction in rock climbing.

Peak counting in surface electromyography signals for quantification of muscle fatigue during dynamic contractions.

This study aimed to assess the utility of peak counting in dynamic muscle contractions. Surface electromyography (sEMG) data were collected from three quadriceps femoris muscles of twelve healthy individuals during 50 repeated isokinetic knee extensions. The level of muscle fatigue was quantified by applying peak counting, mean frequency (MNF), and median frequency (MDF) to sEMG signals, and a fatigue index value was extracted for each parameter. The Bland-Altman plots were used to show the agreement between the methods based on the fatigue index values. The relationship between MNF, MDF and number of peaks (NoP) was described by using linear regression models. The results showed that the peak counting method measures the fatigue level of the muscles equivalent to MNF and MDF in terms of fatigue index values. The peak counting method has a stronger relationship with MNF than MDF, considering the R-squared values of the linear regression models. In conclusion, peak counting was found to be a valid method, and the NoP was evaluated as a reliable parameter in the quantitative analysis of muscle fatigue during dynamic contractions.

Comparison of the Effectiveness of Kinesiology Taping and Rigid Taping on Ankle Kinematics During Drop Landing in Individuals with Lateral Ankle Injury.

BACKGROUND: Lateral ankle sprain is an injury that often occurs during sports or daily life activities. Athletic tape and kinesiology tape applications are among the external support treatment options especially for athletes to support the ankle and protect it from recurrent sprains. We sought to compare the kinematic stabilization effects of different ankle taping applications on the ankle joint during drop landing in individuals with a history of unilateral lateral ankle injury. METHODS: In this randomized controlled study, 30 volunteers with unilateral ankle injury were evaluated. The participants were asked to land on one leg on the involved side and the contralateral side from a 30-cm-high platform. The same practice was repeated after applying kinesiology tape and rigid tape to the injured foot. Kinematic analysis of the foot and ankle was performed by recording three-dimensional spatial position information at a speed of 240 frames per second using infrared cameras. RESULTS: The highest inversion angles of the involved foot at initial contact and 150 msec after initial contact were higher than those of the uninvolved side (P = .03 and P = .04, respectively). There was no significant difference in ankle kinematic values in the involved foot among kinesiology taping, athletic taping, and no taping applications (P = .74). CONCLUSIONS: People with lateral ankle sprains show reduced inversion during landing. There were no significant differences among kinesiology taping, athletic taping, and no taping on the injured foot in terms of ankle kinematics. Care should be taken when using taping materials as protective measures for sports activities.

Effects of beta-blockers on archery performance, body sway and aiming behaviour.

OBJECTIVES: This study aimed to determine the effect of selective (bisoprolol-5 mg) and non-selective (propranolol-40 mg) beta-blockers on archery performance, body sway and aiming behaviour. METHODS: Fifteen male archers participated in a randomised, double-blind, placebo-controlled, cross-over study and competed four times (control, placebo, selective (bisoprolol) and non-selective (propranolol) beta-blocker trials). Mechanical data related to the changes in the centre of pressure during body sway and aim point fluctuation and when shooting was collected. During the shots, heart rate was recorded continuously. RESULTS: Results indicated that, in beta-blocker trials, although shooting heart rates were lowered by 12.8% and 8.6%, respectively, for bisoprolol and propranolol, no positive effect of beta-blockers was observed on shooting scores. Also, the use of beta-blockers did not affect shooting behaviour and body sway. CONCLUSION: The use of either selective or non-selective single dose beta-blockers had no positive effect on shooting performance in archery during simulated match conditions.

The effects of sodium reduction on the gas phase of bread doughs using synchrotron X-ray microtomography.

Globally, the bakery industry has a target of reducing sodium content in bread products. However, removing salt results in changes in the quality of bread through effects on dough's gas phase during the breadmaking process. Using synchrotron X-ray microtomography, the objective of this study was to investigate how sodium reduction induced changes in the gas phase parameters (i.e., gas volume fraction, bubble size distribution (BSD) and its time evolution) of non-yeasted doughs made from a wide range of formulations (i.e., wheat cultivar and water content) prepared with different mixing times. As salt content was reduced, a lower gas volume was retained in the dough by the end of mixing. Less gas bubbles were also retained if doughs were prepared from a stronger wheat cultivar, higher water content, and/or mixed for a shorter time. Rates of change in the median (R0) and the width (ε) of the fitted lognormal radius dependence of bubble volume fraction [BVF(R)] indicated that reduced sodium content permitted disproportionation to proceed more rapidly. Higher water content or longer mixing time also resulted in faster disproportionation, indicating that water content and mixing time can be manipulated as a means of increasing bubble stability against disproportionation during low-sodium breadmaking. An examination of relative changes in dough's gas phase parameters arising from sodium reduction demonstrated that wheat cultivar, water content and mixing time all affected dough's tolerance to sodium reduction. Therefore, attainment of good bread crumb cell structure in low-sodium bread formulas is a function of salt's effects on dough rheology in addition to its effect on yeast activity, so that dough formulation and mixing conditions also need to be considered.

A mechanical model representation of the in vivo creep behaviour of muscular bulk tissue.

In vivo mechanical properties of bulk tissue have not yet been explored sufficiently. One of the major problems researchers face is the lack of agreement between the constitutive models and the standardised methodologies for experimental studies. The object of this study was to obtain bulk modulus of the upper arm under relaxed and controlled contraction that was 25% of the maximum voluntary contraction. A new testing machine was designed to generate constant load on the upper arm and measure the deformation over time. This device is effectively a cuff that applies controllable pressure on a 47-mm wide band of the upper arm. Six different loads (10, 20, 30, 40, 50 and 60 kgf) were applied over a time of up to a maximum of 120 s. The deflection-time curves obtained show strongly non-linear responses of the bulk tissue. The non-linearity manifested by these deflection-time curves is in terms of both time- and load-dependency. A specific mechanical model was developed to represent the creep behaviour of the bulk tissue. The creep behaviour of the upper arm can be simulated by using four Voigt viscoelastic models in series. The three obvious soft tissues of the upper arm, namely skin, fat and muscle, were modelled in series. The effects of blood vessels and connective tissue were also modelled in series with the previous ones. A mechanical model would provide a more controlled method of studying the mechanical properties of the bulk tissue. The purpose of the current research, therefore, was to develop a mechanical model, which would predict the non-linear, viscoelastic behaviour of the human muscular bulk tissue.

Semitendinosus snapping: analysis of movement, electromyographic activities, muscle strength and endurance, motor control and joint position sense.

A female ballet with a history of two-years of semi-tendinosus (ST) snapping was assessed. On physical examination snapping was observed during hyperextension of the knee. Neither any history of trauma nor treatment was recalled. Magnetic resonance imaging (MRI), movement analysis, onset timing of ST and Bisceps Femoris (BF), motor control, isokinetic muscle strength and endurance, joint position sense (JPS) were assessed. The MRI findings were normal. There were abnormal oscillations observed during hyperextension of the snapping knee compared to healthy side. There were no isokinetic muscle strength nor do muscle endurance differences. The motor control and JPS deficits were greater on the snapping knee than the healthy side. ST onset timing was earlier than BF on the snapping side. Snapping of the semitendinosus tendon has an adverse affect on JPS, motor control and onset timing of the knee muscles.

Fusionless instrumentation in growing spine and adjacent segment problems: an experimental study in immature pigs.

STUDY DESIGN: Experimental study. OBJECTIVE: To compare the effects of fusionless instrumentation (FI) and instrumented fusion (IF) on the adjacent segment in an immature pig model. SUMMARY OF BACKGROUND DATA: Observations reveal proximal junctional kyphosis after FI. Possible reasons are stress concentration, repeated distractive forces, and/or soft tissue damage done in the index surgery. It was speculated that FI can decrease stressors to the junctional area by preserving the spinal mobility in some manner; however, this has not been proven to date. METHODS: Thirteen piglets of 10- to 14-week age were used. FI and IF were performed on 7 and 3 piglets, respectively, and 3 piglets formed the control group. Control piglets did not undergo any surgical procedures. T11-L4 instrumentation, decortication, and grafting were applied to IF piglets. In FI groups, however, L1-L2 was left uninstrumented and unfused using T11-T12 and L3-L4 levels as anchors to the growing construct. A total of 4 lengthening procedures were performed: 1 in the index operation and 3 more, once in each lengthening procedure monthly, for 3 months. Four months after the index operations, all piglets were killed and the adjacent segment motion capabilities, disc, and facets were evaluated with radiographical, magnetic resonance imaging, biomechanical, and histological analyses. RESULTS: Comparison of proximal junctional Cobb angles of the postindex (mean: 21, range: 17-27) and presacrification (mean: 21, range: 11-31) radiographs in the FI group revealed no difference (P> 0.05). In magnetic resonance imaging, both surgical group proximal adjacent discs showed degeneration to some degree that was statistically indifferent (P = 0.903). Biomechanical evaluation revealed restriction of adjacent segment motion in all directions for both groups; however, this negative effect was significantly less in FI group (P < 0.01). Degeneration observed in histological evaluation in adjacent discs and facets of FI group was significantly lower (P = 0.00). CONCLUSION: In this quadruped straight spine model, in comparison with IF applications, FI is closer to normal physiology even after several lengthening procedures regarding the adjacent segment discs, facet joints, and motion, when interpreting the radiological, biomechanical, and histological results altogether.

The in vivo mechanical properties of muscular bulk tissue.

The aim of this study was to characterize the bulk modulus properties of the upper arm under relaxed and controlled contraction which is defined as 25% of the maximum voluntary contraction. A new testing machine was designed to generate a continually increasing load on the upper arm and measure the load over time. The machine consists of a device which is effectively a cuff that applies controllable pressure on a 47 mm wide band of the upper arm. A set of four different constant strain rates was used to test the stiffness of the arm bulk tissue. The stress-strain test consisted of 0.5, 1, 2, and 4 mm.s(-1) constant strain rates. The stress-strain curves obtained show strongly non-linear response of the bulk tissue. The nonlinearity is evident that the stress-strain curve for bulk tissue is time dependent.