Kathleen M. Knutzen

A Biomechanical Analysis of Four Sprint Start Positions

The sprint starts of 12 skilled collegiate sprinter/hurdlers were filmed for four different sprint start conditions. Ground reaction forces were collected for the first step out of the blocks and velocities through a 2-m speed trap immediately following the first support phase were recorded. The subjects employed their preferred right-left leg placement in the blocks, while the anterior-posterior spacing of the front block with respect to the starting line and the amount of forward lean in the set position were varied. Four positions were constructed that accounted for anthropometric differences. The four positions consisted of combinations of two arm orientations (forward lean and perpendicular to ground) and two front block to starting line distances (bunched and elongated). Kinematic data were reduced to provide center of mass position and velocity measures and analyzed for critical periods throughout the starting action. Selected critical events from the first step kinetic records were also analyzed. The results indicated that the elongated starting positions resulted in greater horizontal displacement, greater propelling impulse, increased first step toe-off velocity, and greater average velocity through a 2-m speed trap. Arm orientation effects were less well defined. Forward lean tended to result in greater vertical velocity at block clearance and horizontal velocity at first step toe-off, whereas perpendicular arm positioning resulted in greater 2-m speed trap velocity.

Sit-to-Stand Performance of Older Adults following Strength Training

Abstract A group of healthy older adults completed an 8-week resistance-training program. For 38 participants (14 men, 24 women; ages 60–90 years; M mass = 73.2 kg, SD = 12.3; M height = 1.65 m, SD = 0.08), pre- and postprogram sit-to-stand performance was analyzed (60 Hz video) focusing on center of mass kinematics surrounding transition. Significant changes were attributed to improved strength. Peak forward, downward, and upward velocities increased (16, 59, and 26%, respectively), and relative transition time was delayed 27%. These behaviors were more similar to those of healthy younger adults. Results also indicated strategy changes. Participants exploited their improved strength, forming a distinctive movement pattern emphasizing stability followed by a brisk rise. These adaptations represent meaningfully improved function in an important daily living activity.

A biomechanical analysis of two functional knee braces.

The influence of knee bracing was evaluated during the activity of running by examining ground reaction forces and knee joint movement parameters assessed electrogoniometrically. Twenty-one subjects were assigned to 1 of 3 groups based on medical records provided by a physician: normal or non-injury group; anterior cruciate ligament lesion/laxity group; and anterior cruciate ligament repair group. Four test conditions were investigated: healthy or control limb; injured or experimental limb; Generation II knee brace; and Marquette Knee Stabilizer knee brace. Ten running trials were performed for each condition at a photoelectrically controlled running pace (3.33 +/- 0.11 m X s-1). There were no significant differences as a result of group membership for both electrogoniometer and force platform analyses (P less than 0.05). There was a significant difference across the four test conditions. Both knee brace applications were shown to significantly reduce knee flexion during swing and support, total rotation, and total varus/valgus movement parameters of the experimental knee joint. Both brace applications were also shown to alter the experimental limb by increasing the relative time to the achievement of the initial collision force, creating a greater collision force and thereby creating larger impulses in both the vertical and foreaft directions during the initial contact phase.

Effect of strength training on orthostatic hypotension in older adults.

PURPOSE This preliminary study attempted to identify the frequency of orthostatic hypotension (OH) in community dwelling older adults who volunteered to participate in an 8-week, heavy-resistance, strength-training program. It also assessed the effect of the strength-training program on OH. METHODS From a larger study (n = 53) on high-resistance strength training in older adults (mean age 71.4 +/- 6.6 years), a subset of subjects (n = 24), mean age 71.0 +/- 5.8 years, was evaluated who met at least one criterion for OH. All subjects were tested for resting blood pressures (BP) and heart rates (HR) in the supine, sitting, and standing positions. Also noted was their response to orthostatism in rising from a cot after 10 minutes and rising from a chair after 5 minutes. The subset was not different from the overall group in gender ratio, age, or effect of medication on BP. The treatment was an 8-week strength-training program at 80% of their one repetition maximum. RESULTS Significant changes (P < 0.05) were shown in supine diastolic BP (+3.2 mm Hg), sitting systolic BP (-3.9), and standing HR (+4.9 beats per minute). In response to the orthostatic challenge, significant (P < 0.05) improvements were shown in systolic BP (+9.7 mm Hg), diastolic BP (+4.7), and HR (+3.2 beats per minute) for the rise from chair, and in diastolic BP (+6.7 mm Hg) rise from the cot. CONCLUSIONS These data show that OH is not uncommon (45%) in community dwelling older adults. A strength training program in older adults has little effect on resting BP, but elicits a positive adaptation to an orthostatic challenge.

Effect on performance of learning a pilates skill with or without a mirror

Mirrors are often used in an instructional environment where precise movements must be learned (e.g., martial arts, Pilates, dance). The potential for mirrors in the learning environment of a Pilates class, to affect the subsequent performance of a Pilates star movement when mirrors are not present, was examined. Twenty subjects learned the Pilates star movement over seven weeks, either with (n=11) or without (n=9), mirrors present in the Pilates studio. Performance of the star without mirrors present was assessed quantitatively before and after the training, by video analysis of the degree of lateral straightness of the subjects body at the start, middle, and end of the star movement. Performance of the star movement without a mirror present improved similarly for both the group that learned with, and the group that learned without, mirrors present (p<0.05). These results indicate that the inclusion of mirrors in a learning environment, to provide immediate visual feedback during learning, does not necessarily enhance the subsequent performance of a skill when mirrors are not present.

Magnesium-creatine supplementation effects on body water

This study evaluated magnesium-creatine (MgCre) supplementation on body water and quadriceps torque. Maltodextran (Placebo), Mg oxide plus Cre (MgO-Cre), and Mg-creatine chelate (MgC-Cre) at 800 mg Mg and 5 g Cre per day were used for 2 weeks in 35 subjects in a random assignment, blinded study. Pre-post measures were completed with bioimpedance to determine total body water (TBW), extracellular water (ECF), and intracellular water (ICF), and an isokinetic device at 180 degrees per second for knee extension peak torque (T), total work (W), and power (PWR). Body weights increased for both treatment groups, MgO-Cre Delta 0.75 kg (P <.05) and MgC-Cre Delta 0.4 kg (P =.07). Significant pre-post differences (P <.05) were noted only for MgC-Cre in ICW (26.29 v 28.01 L) and ECW (15.75 v 14.88 L). MgC-Cre had significant peak T (Nm) increase (124.5 v135.8, P <.05), while MgO-Cre (116.4 v 124.9, P =.06) and placebo (119.8 v 123.7, P =.343) did not. Both treatment groups had increased PWR (P <.05). MgC-Cre affects cellular fluid compartments. The peak torque changes were significant only in the MgC-Cre group, which had increases in ICW that may infer more muscular creatine due to its osmotic effect, and with increased cellular hydration, perhaps increased protein synthesis.

Influence of Ramp Position on Joint Biomechanics During Elliptical Trainer Exercise

Introduction: The elliptical trainer, developed to simulate running while minimizing joint loads, elicits a unique lower extremity biomechanical response. The purpose of this study was to examine the angular kinematics, peak net joint moments, and peak joint powers at the hip, knee and ankle joints while exercising at three different ramp settings on the elliptical trainer exercise machine (Precor EFX). Methods: Twenty-six healthy individuals with no history of lower extremity injury and with previous experience exercis- ing on an elliptical trainer volunteered for this study. Motion was captured with two cameras as subjects performed exer- cise at three ramp conditions. The pedal resistance was kept constant at the lowest setting. The pedals of the elliptical were fitted with three orthogonal load cells. Video and force data were synchronized and used to perform a 2D inverse dynamics analysis. Results: As the ramp inclination increased, subjects demonstrated greater amounts of ankle dorsiflexion, knee flexion, hip flexion and lesser degrees of plantar flexion and hip extension (p <.000). Mean peak moments at the ankle joint were not significantly different across the ramp settings, but peak knee extensor and hip flexor moments increased while knee flexor and hip extensor at the hip decreased (p <.000). As the ramp inclination increased, peak positive power at both the knee and hip significantly decreased and negative power decreased at the knee joint (p <.000), though the effect size for these changes was small. Conclusions: The hip and knee joints were observed as the primary sources of power during exercise on the elliptical trainer at the lowest resistance setting.

Ambulatory characteristics of the visually disabled

Ground-reaction force patterns were examined in three groups: sighted, blindfolded, and blind. Fifteen subjects, aged 19 to 41, participated in the study. Ten walking trials were collected over a 5-meter distance. The data were analyzed by normalization for body weight, extraction of specific ground-reaction force parameters through force-time curve analysis routines, and averaging across the ten trials for each subject. Results of a one-way analysis of variance indicated that there were no significant differences when force patterns were analyzed in terms of mediolateral and vertical ground-reaction force components. Blind subjects were shown to have significantly greater (p < 0.05) maximum braking and propelling forces.

Effect of Inspiratory Muscle Training and Core Exercise Training on Core Functional Tests: 3164

Brilla LB, Kauffman TH. Effect of Inspiratory Muscle Training and Core Exercise Training on Core Functional Tests. JEPonline 2014;17(3):12-20. This study tested the effects of inspiratory muscle training on core function compared to a typical core training program. Subjects consisted of 32 healthy, recreationally active individuals (18-25 yrs of age) who were randomly assigned to one of three groups: Control (C), Inspiratory Muscle Training (IMT), and Core Exercise Class (AbEx). IMT performed inspiratory muscle training for 6 wks at 85% maximal inspiratory pressure (MIP), while AbEx performed standard core training of the same duration. Core function was assessed preand post-training using a side bridge, prone extension and Stabilizer test of transversus abdominis (TrA) function. MIP was also assessed before and after the treatment. Significant interaction effect was observed for MIP (P≤0.05). IMT MIP increased from 1.06 ± 0.37 to 1.71 ± 0.41 cm H2O (P≤0.05) with no significant pre-post changes in C (1.09 ± 0.29 to 1.15 ± 0.36 cm H2O) or AbEx (0.78 ± 0.31 to 0.88 ± 0.33 cm H2O). A significant interaction effect was noted in prone extension (P≤0.05). Time increased in AbEx from 114.0 ± 53.0 to 154.0 ± 77.6 sec (P≤0.05), with no significant changes in C (158.9 ± 75.5 to 152.1 ± 62.6 sec) or IMT (132.0 ± 39.2 to 132.8 ± 40.3 sec). A significant interaction for the Stabilizer test of TrA function was found (P≤0.05). The IMT group improved from -6.9 ± 12.6 to -10.0 ± 11.0 mmHg (P≤0.05), with no significant changes in the Control (-5.0 ± 12.1 to -4.8 ± 13.4 mmHg) or AbEx groups (-15.0 ± 5.8 to -9.7 ± 10.4 mmHg). There were no significant differences (P≥0.05) in the side bridge test. Six weeks of core training and inspiratory muscle training improve core function and target different muscles.