Sasho J. Mackenzie

Neuromuscular Adaptations Following Antagonist Resisted Training

MacKenzie, SJ, Rannelli, LA, and Yurchevich, JJ. Neuromuscular Adaptations Following Antagonist Resisted Training. J Strength Cond Res 24(1): 156-164, 2010-The purpose was to assess a novel form of strength training, antagonist resisted training (ART), with potential use in microgravity and athletic rehabilitation settings. ART uses the force from antagonist muscles, during cocontractions, as the source of resistance for the agonists. Strength and electromyography (EMG) measurements were recorded before and after a 6-week training program during which participants trained the left arm while the right arm served as a control. Training was designed so that the elbow extensors (antagonists) served as resistance for the elbow flexors (agonists). Elbow flexor and extensor strengths were measured during maximal isometric contractions with the elbow fixed at 90 degrees. EMG was recorded from the biceps brachii and lateral head of the triceps brachii during all strength tests. EMG was also recorded from both muscles during a maximal isometric cocontraction of the elbow flexors and extensors. Elbow flexion strength increased significantly for the trained arm (5.8%) relative to the control (0.5%) (p = 0.003). Elbow extension strength of the trained limb also increased significantly (8.5%) relative to the control (4.5%) (p = 0.029). Biceps and triceps EMG, during maximum strength tests, increased significantly for the trained arm (18.5 and 18.6%) relative to the control (0.5 and −5.2%) (p = 0.035 and p = 0.01). Biceps and triceps EMG, during maximum cocontraction tests, increased significantly for the trained arm (30.1 and 61.1%) relative to the control (9.2 and 1.1%) (p = 0.042 and p = 0.0005). ART was found to increase strength and therefore could be an effective form of resistance training. Because it requires no equipment, ART may be especially applicable in microgravity environments, which have space and weight constraints.

Validity and reliability of a new method for measuring putting stroke kinematics using the TOMI® system

Abstract The purpose of this study was to determine the validity and reliability of a new method for measuring three-dimensional (3D) putting stroke kinematics using the TOMI® device. A putting robot and a high-speed camera were used to simultaneously collect data for the validity evaluation. The TOMI® device, when used in conjunction with standard 3D coordinate data processing techniques, was found to be a valid and reliable method for measuring face angle, stroke path, putter speed, and impact spot at the moment of ball contact. The validity of the TOMI® measurement system was quantified using the 95% limits of agreement method for each aforementioned variable. The practical significance of each validity score was assessed by incorporating the maximum estimated measurement error into the stroke of the putting robot for 10 consecutive putts. All putts were executed from a distance of 4 m on a straight and flat synthetic putting surface. Since all putts were holed successfully, the measurement error for each variable was deemed to be negligible for the purposes of measuring putting stroke kinematics. The influence of key kinematic errors, at impact, on the outcome of a putt was also determined.

A biomechanical comparison of the vertical jump, power clean, and jump squat

Abstract The purpose of this study was to compare the kinetics, kinematics, and muscle activation patterns of the countermovement jump, the power clean, and the jump squat with the expectation of gaining a better understanding of the mechanism of transfer from the power clean to the vertical jump. Ground reaction forces, electromyography, and joint angle data were collected from 20 trained participants while they performed the three movements. Relative to the power clean, the kinematics of the jump squat were more similar to those of the countermovement jump. The order in which the ankle, knee, and hip began extending, as well as the subsequent pattern of extension, was different between the power clean and countermovement jump. The electromyography data demonstrated significant differences in the relative timing of peak activations in all muscles, the maximum activation of the rectus femoris and biceps femoris, and in the activation/deactivation patterns of the vastus medialis and rectus femoris. The greatest rate of force development during the upward phase of these exercises was generated during the power clean (17,254 ), which was significantly greater than both the countermovement jump (3836 ) and jump squat (3517 ) conditions (P < .001, ).

Dual-Energy X-Ray Absorptiometry to Measure the Influence of a 16-Week Community-Based Swim Training Program on Body Fat in Children and Adolescents With Intellectual Disabilities

OBJECTIVE To use dual-energy x-ray absorptiometry (DXA) to measure the effects of a 16-week community-based swim training program on percent body fat in children and adolescents with intellectual disability (ID). DESIGN Convenience sample. SETTING University sport complex and exercise science laboratory. PARTICIPANTS Children and adolescents (n=8; mean age +/- SD, 13.1 +/- 3.4 y), 2 girls and 6 boys with ID, of varying fat levels (11%-35%). INTERVENTION A swim training program lasting for the duration of 16 weeks with three 1-hour sessions held at a 25-m pool each week. MAIN OUTCOME MEASURE Assessing percent body fat at pretest and posttest through the use of DXA. RESULTS After the 16-week exercise training program, we observed a 1.2% median increase in body fat percentage with a range from -0.3% to 4.5%. Wilcoxon matched-pairs signed-ranks tests suggest that these results are statistically significant (P=.039; exact). CONCLUSIONS Exercise training alone proved ineffectual in reducing percent body fat in 8 children and adolescents with ID. Further research should consider implementing a combined diet and exercise program. To gauge the effectiveness of intervention programs, valid methods and complex measurement tools such as DXA should be used to assess changes in percent body fat in such a heterogeneous population.

Visually focusing on the far versus the near target during the putting stroke

Abstract The purpose was to evaluate the traditional method, of visually focusing on the ball, in comparison to focusing on the hole, during the putting stroke. The study design consisted of a pretest, a 4-week practice period, and a posttest. Participants (n = 31, handicap: 18.7 ± 10.4) practised using only one of the two gaze techniques. Testing consisted of having all participants putt using both gaze techniques from both a 1.22 m and a 4 m distance. Five putts were executed for each gaze technique/putt length combination for a total of 20 putts in each testing session per participant. The kinematics of every putting stroke executed during testing (1240 strokes) were captured using a TOMI® system. There was a significant improvement in putting success for both groups following practice (P = 0.001). Practising while visually focusing on the hole, resulted in a statistically significant reduction in putter speed variability in comparison to practising while visually focusing on the ball (P = 0.017). Visually focusing on the hole did not meaningfully (nor statistically) affect the quality of impact as assessed by the variability in face angle, stroke path, and impact spot at the precise moment the putter head contacted the ball.

Club position relative to the golfer's swing plane meaningfully affects swing dynamics

Previous research indicates that the motion of the golf club is not planar and that the plane traced out by the club is different than that of the golfers hands. The aim of the present study was to investigate how the position of the club, relative to the golfers swing plane, influences the motion of the club by using a four-segment (torso, upper arm, forearm, and club), three-dimensional forward dynamics model. A genetic algorithm optimized the coordination of the models four muscular torque generators to produce the best golf swings possible under six different conditions. The series of simulations were designed to demonstrate the effect of positioning the club above, and below, the golfers swing plane as well as the effect of changing the steepness of the golfers swing plane. The simulation results suggest that positioning the club below the golfers swing plane, early in the downswing, will facilitate the squaring of the clubface for impact, while positioning the club above the plane will have the opposite effect. It was also demonstrated that changing the steepness of the golfers swing plane by 10° can have little effect on the delivery of the clubhead to the ball.

Evaluation of the plumb-bob method for reading greens in putting.

This study evaluated the validity of the plumb-bob method as used to determine the break of a putt. Two separate experiments were conducted to examine the consequence of violating inherent assumptions in the method. In the first experiment, a controlled putting environment was constructed to assess the plumb-bob method in determining the break of a putt, if the slope of the green was not constant from the position of the golfer behind the ball through to the hole. It was determined that if the slope of the green beneath the golfer was different from the slope between the ball and the hole, then the plumb-bob method would provide an incorrect indication of break. The second experiment examined the ability of a golfer to stand perpendicular to a slope. Half of the participants in the study deviated by ± 1.5° or greater from standing perpendicular to a slope. A + 1.5° error on a 1.4 m (∼ 4.5 ft) putt translates into reading an extra 0.08 m of break and a missed putt. The plumb-bob method was found to be an invalid system for determining the break of a putt.

Dual-Energy X-Ray Absorptiometry to Measure the Effects of a Thirteen-Week Moderate to Vigorous Aquatic Exercise and Nutritional Education Intervention on Percent Body Fat in Adults with Intellectual Disabilities from Group Home Settings

Dual-Energy X-Ray Absorptiometry to Measure the Effects of a Thirteen-Week Moderate to Vigorous Aquatic Exercise and Nutritional Education Intervention on Percent Body Fat in Adults with Intellectual Disabilities from Group Home Settings People with intellectual disability are more likely to be obese and extremely obese than people without intellectual disability with rates remaining elevated among adults, women and individuals living in community settings. Dual-energy X-ray absorptiometry measured the effects of a 13-week aquatic exercise and nutrition intervention on percent body fat in eight adults with intellectual disabilities (aged 41.0 ± 13.7 yrs) of varying fat levels (15%-39%) from two group homes. A moderate to vigorous aquatic exercise program lasted for the duration of 13 weeks with three, one-hour sessions held at a 25m pool each week. Nutritional assistants educated participants as to the importance of food choice and portion size. A two-tailed Wilcoxon matched-pairs signed-ranks test determined the impact of the combined intervention on body fat percentage and BMI at pre and post test. Median body fat percentage (0.8 %) and BMI (0.3 kg/m2) decreased following the exercise intervention, but neither were statistically significant, p = .11 and p = .55, respectively. The combined intervention was ineffective at reducing percent body fat in adults with intellectual disability according to dual-energy X-ray absorptiometry. These results are in agreement with findings from exercise alone interventions and suggest that more stringent nutritional guidelines are needed for this population and especially for individuals living in group home settings. The study did show that adults with intellectual disability may participate in moderate to vigorous physical activity when given the opportunity.

The influence of golf shaft stiffness on grip and clubhead kinematics

ABSTRACT The purpose of this study was to investigate the influence of shaft stiffness on grip and clubhead kinematics. Two driver shafts with disparate levels of stiffness, but very similar inertial properties, were tested by 33 golfers representing a range of abilities. Shaft deflection data as well as grip and clubhead kinematics were collected from 14 swings, with each shaft, for each golfer using an optical motion capture system. The more flexible shaft (R-Flex) demonstrated a higher contribution to clubhead speed from shaft deflection dynamics (P < .001), but was also associated with significantly less grip angular velocity at impact (P = .001), resulting in no significant difference in clubhead speed (P = .14). However, at the individual level, half of the participants demonstrated a significant difference in clubhead speed between shafts. The more flexible shaft was also associated with significantly different magnitudes of head rotation relative to the grip. More specifically, both bend loft (P < .001) and bend lie (P < .001) were greater for the R-Flex shaft, while bend close (P = .017) was greater for the stiffer (X-Flex) shaft. However, changes in grip orientation resulted in no significant differences in face orientation, between the shafts, at impact.

The influence of golf shaft torque on clubhead kinematics and ball flight

ABSTRACT The purpose of this study was to investigate the influence of shaft torque (torsional rigidity) on clubhead kinematics and the resulting flight of the ball. Two driver shafts with disparate levels of torque, but otherwise very similar properties, were tested by 40 right-handed golfers representing a range of abilities. Shaft deflection data as well as grip and clubhead kinematics were collected from 14 swings, with each shaft, for each golfer using an optical motion capture system. Ball flight and additional clubhead kinematics were collected using a Doppler radar launch monitor. At impact, the high torque shaft (HT) was associated with increased delivered loft (P = .028) and a more open face (P < .001) relative to the low torque shaft (LT). This resulted in the HT shaft being associated with a ball finishing position that was further right (P = .002). At the individual level, the change in face angle due solely to shaft deformation was significantly higher for the HT shaft for 25/40 participants. Although shaft twist was not directly measured, it was logically deduced using the collected data that these outcomes were the result of the HT being twisted more open relative to the LT shaft at impact.