Guillermo J. Noffal

The Reliability and Validity of a Chair Sit-and-Reach Test as a Measure of Hamstring Flexibility in Older Adults

The purpose of this study was to examine the test-retest reliability and the criterion validity of a newly developed chair sit-and-reach (CSR) test as a measure of hamstring flexibility in older adults CSR performance was also compared to sit-and-reach (SR) and back-saver sit-and-reach (BSR) measures of hamstring flexibility. To estimate reliability, 76 men and women (M age = 70.5 years) performed the CSR on 2 different days, 2-5 days apart. In the validity phase of the study, scores of 80 men and women (M age = 74.2 years) were obtained on three field test measures of hamstring flexibility (CSR, SR, and BSR) and on a criterion test (goniometer measurement of a passive straight-leg raise). Results indicate that the CSR has good intraclass test-retest reliability (R = .92 for men; r = .96 for women), and has a moderate-to-good relationship with the criterion measure (r = .76 for men; r = .81 for women). The criterion validity of the CSR for the male and female participants is comparable to that of the SR (r = .74 and r = .71, respectively) and BSR (r = .70 and r = .71, respectively). Results indicate that the CSR test produces reasonably accurate and stable measures of hamstring flexibility. In addition, it appears that the CSR is a safe and socially acceptable alternative to traditional floor sit-and-reach tests as a measure of hamstring flexibility in older adults.

Isokinetic Eccentric-to-Concentric Strength Ratios of the Shoulder Rotator Muscles in Throwers and Nonthrowers

Background One of the possible mechanisms leading to shoulder injury may be a strength imbalance between those muscles that accelerate the upper limb and those responsible for deceleration. Many studies have examined shoulder balance through a concentric strength ratio of external and internal shoulder rotator muscles. Hypothesis A functional external eccentric-to-internal concentric ratio may be a better identifier of muscular imbalance in dominant and nondominant shoulders of throwers and nonthrowers. Study Design Controlled laboratory study. Methods Eccentric external and concentric internal peak torques were measured bilaterally in 59 men (16 throwers and 43 nonthrowers) at 300 deg/sec. Subjects were tested in the supine position with the shoulder abducted to 90° and the elbow flexed to 90°. Results Throwers exhibited significantly lower ratios than nonthrowers in their dominant limb; there was no difference between groups for the nondominant limb. Conclusions The lower ratio in the throwers’ dominant limb was attributed to significantly greater concentric internal rotation torques without concomitant eccentric external torque gains. Clinical Relevance Rehabilitation and injury prevention regimens that include functional exercises to improve eccentric external rotation strength may bring more balance to the dominant shoulder of throwing athletes.

Stretching has no effect on tennis serve performance.

&NA; Knudson, D.V., G.J. Noffal, R.E. Bahamonde, J.A. Bauer, and J.R. Blackwell. Stretching has no effect on tennis serve performance. J. Strength Cond. Res. 18(3):654–656. 2004.—Stretching prior to vigorous physical activity has been shown to decrease high‐force muscular performance, but little is known about the effect of stretching on speed and accuracy movements. Serving percentage and radar measurements of ball speed were studied to examine the acute effect of stretching on tennis serve performance. Eighty‐three tennis players from beginning level to advanced volunteered to serve following traditional (T) warm‐up and traditional plus stretching (S) conditions. Service speeds and service percentage of each condition were measured. Dependent t‐tests showed nonsignificant effects of stretching on service speed (p = 0.06) or accuracy (p = 0.35), and this lack of an effect was similar for all skill levels, age, and gender. The large sample and good statistical power in this study indicated that these observations are not likely type II errors. There was no short‐term effect of stretching in the warmup on the tennis serve performance of adult players, so adding stretching to the traditional 5‐minute warm‐up in tennis does not affect serve performance.

Relationship Between Force-time and Velocity-time Characteristics of Dynamic and Isometric Muscle Actions

Khamoui, AV, Brown, LE, Nguyen, D, Uribe, BP, Coburn, JW, Noffal, GJ, and Tran, T. Relationship between force-time and velocity-time characteristics of dynamic and isometric muscle actions. J Strength Cond Res 25(1): 198-204, 2011-Previous research has investigated the force-time curve characteristics of isometric and dynamic muscle actions; however, few studies have addressed their relationship to dynamic exercise velocity-time variables. The purpose of this study was to investigate relationships between velocity-time characteristics (high pull and vertical jump peak velocity and rate of velocity development [HPPV, HPRVD, VJPV, VJRVD]), force-time characteristics (isometric peak force [IsoPF], body mass adjusted isometric peak force [IsoPF/BM], isometric rate of force development at different millisecond windows [IsoRFD50-250], dynamic peak force [HPPF], body mass adjusted dynamic peak force [HPPF/BM]), and vertical jump height (VJHeight). Nineteen recreationally trained men (age 23.89 ± 2.92 yr; height 176.32 ± 7.06 cm; mass 78.76 ± 16.50 kg) completed 2 testing sessions. The first session consisted of 3 isometric mid-thigh pulls on a force plate with each repetition held for 3 seconds. On the second testing session, subjects completed 3 dynamic mid-thigh high pulls with 30% IsoPF followed by 3 vertical jumps on a force plate. The HPRVD correlated with IsoRFD50 (r = 0.52) and IsoRFD100 (r = 0.49). The HPPV correlated with IsoPF/BM (r = −0.60), IsoRFD50 (r = 0.56), and IsoRFD100 (r = 0.56). The VJHeight correlated with IsoPF/BM (r = 0.61), whereas VJPV correlated with IsoPF/BM (r = 0.62). These correlations suggest that explosive isometric force production within 50 to100 milliseconds may influence the ability to accelerate an implement or body and attain high velocity, albeit in a moderate fashion. In addition, body mass adjusted strength may positively influence vertical jump parameters.

Effects of velocity-specific training on rate of velocity development, peak torque, and performance.

Little is known about the velocity-specific adaptations to training utilizing movement velocities in excess of 300°·s-1. The purpose of this investigation was to determine the effects of 4 weeks of slow (60°·s-1) vs. fast (400°·s-1) velocity training on rate of velocity development (RVD), peak torque (PT), and performance. Twenty male kinesiology students (22.0 years ± 2.72; 178.6 cm ± 7.1; 82.7 kg ± 15.5) were tested, before and after 4 weeks of training, for PT production, RVD (at 60, 180, 300, 400, and 450°·s-1), standing long jump (SLJ) distance, and 15- and 40-m sprint times. All participants underwent 8 training sessions, performing 5 sets of 5 repetitions of simultaneous, bilateral, concentric knee extension exercises on a Biodex System 3 isokinetic dynamometer at either 60° or 400° per second. Two 5 (speed) X 2 (time) X 2 (group) multivariate repeated measures analyses of variance revealed no significant differences between groups on any measure. Therefore, the groups were collapsed for analysis. There was a significant (p > 0.05) main effect for RVD by time and SLJ distance by time (pre- 227.1 cm ± 21.2; post- 232.9 cm ± 20.7) but no significant change in PT or 15- or 40-m sprint times. These results offer support for the suggestion that there is a significant neural adaptation to short-term isokinetic training performed by recreationally trained males, producing changes in limb acceleration and performance with little or no change in strength. Because results were independent of training velocity, it appears as though the intention to move quickly is sufficient stimulus to achieve improvements in limb RVD. Changes in SLJ distance suggest that open kinetic chain training may benefit the performance of a closed kinetic chain activity when movement pattern specificity is optimized.

Development and evaluation of a biomechanics concept inventory

Abstract To help instructors in evaluating innovations in biomechanics instruction, a standardised test of the key concepts taught in the introductory biomechanics course was developed. The Biomechanics Concept Inventory (BCI) consists of 24 questions that test four prerequisite competencies and eight biomechanics competencies. Three hundred and sixty seven students from ten universities throughout the United States took the test at the beginning and the end of the introductory biomechanics course. Analysis of a sub‐sample of the students showed that the BCI was reliable with typical errors in internal consistency and test‐retest conditions of 1.4 and 2.0 questions, respectively. Mean pre‐test scores (8.5 ± 2.0) significantly (p < 0.0001) improved to 10.5 ± 3.2 in the post‐test (n = 305). Typical biomechanics students could correctly answer half of the prerequisite questions on the pre‐test. Instruction resulted in a mean normalised gain (g) of 13.0% of maximum possible improvement that was consistent with research on traditional instruction in introductory physics courses. It was concluded that the BCI could be an effective tool to evaluate the overall effect of pedagogical strategies on student learning of key biomechanical concepts in the introductory biomechanics course.

Effect of a Dynamic Loaded Warm-Up on Vertical Jump Performance

Chattong, C, Brown, LE, Coburn, JW, and Noffal, GJ. Effect of a dynamic loaded warm-up on vertical jump performance. J Strength Cond Res 24(7): 1751-1754, 2010-Considering the importance of the vertical jump in several sports, an optimal warm-up protocol may help athletes perform at their maximum level. The purpose of this study was to investigate the potentiating effects of different levels of external resistance (weighted vest) during box jumps on vertical jump performance. Twenty resistance trained men (age 22.45 ± 1.73 years, height 176.83 ± 6.67 cm, mass 76.98 ± 8.56 kg) participated in this study. Subjects performed 5 jumps onto a box equivalent in height to their lateral femoral condyle. After a 2-minute rest period, subjects performed 3 vertical jumps with the greatest height being recorded. On day 1, each subject performed a control condition with no external resistance to establish a baseline vertical jump height. On the following days, they performed 4 random jump conditions with a weight vest equivalent to 5, 10, 15, or 20% of their body weight then rested for 2 minutes before performing 3 posttest vertical jumps. Results demonstrated no significant interaction of condition by time for vertical jump height. However, there was a significant main effect for time (p < 0.05) with posttest jump height (22.99 ± 3.35 in.) being greater than pretest jump height (22.69 ± 3.37 in.). Performing an active dynamic warm-up with or without a weighted vest produced significantly greater posttest vertical jump performance. A dynamic warm-up may improve vertical jump performance, albeit to a very small increment.

Lower Extremity Biomechanics During a Regular and Counterbalanced Squat

Abstract Lynn, SK and Noffal, GJ. Lower extremity biomechanics during a regular and counterbalanced squat. J Strength Cond Res 26(9): 2417–2425, 2012—If the efficiency of human movement patterns could be improved using exercise, this could lead to more effective musculoskeletal disease-injury prevention and rehabilitation programs. It has been suggested that an efficient squat movement pattern emphasizes the use of the large hip extensors instead of the smaller knee extensors. The purpose of this study was to determine whether a counterbalanced squat (CBS) could produce a more hip-dominant and less knee-dominant squat movement pattern as compared with a regular squat (RS). There were 31 recreationally trained college-aged participants (15 male, 16 female) who performed 10 squats (5 CBS and 5 RS), while segment kinematics, ground reaction forces, and muscle (gluteus maximus [GM], quadriceps, hamstrings) electromyographic (EMG) activations were recorded. Peak sagittal plane net joint moments and joint ranges of motion at the hip, knee, and ankle joints along with peak and integrated EMG activation levels for all 3 muscles were compared using analysis of variance (squat type × sex). The results revealed that the CBS increased the hip joint moment and GM activation, while it decreased the knee joint moment and quadriceps activation as compared with the RS. Therefore, the CBS produces a more hip-dominant and less knee-dominant squat movement pattern and could be used in exercise programs aimed at producing more hip-dominant movement patterns.

Performance differences between sexes in the pop-up phase of surfing.

Eurich, AD, Brown, LE, Coburn, JW, Noffal, GJ, Nguyen, D, Khamoui, AV, and Uribe, BP. Performance differences between sexes in the pop-up phase of surfing. J Strength Cond Res 24(10): 2821-2825, 2010-Surfing is a dynamic sport that is multidirectional in nature and requires peak performance in variable ocean conditions. Its growing popularity among the female population has stirred curiosity as to whether women can and will 1 day face their male counterparts in head-to-head competition at the top levels. The purpose of this study was to examine male and female differences in performance of a simulated surfing pop-up movement. Forty recreationally trained surfers (20 men and 20 women) were instructed to lie prone on a force plate, in the pop-up position (similar to a push-up), with only their hands in contact with the plate. A velocity transducer was attached to their back via an adjustable strap around their upper trunk. They completed 3 pop-ups as explosively as possible by pushing forcefully with their hands and jumping to their feet. Absolute and relative force and power were measured. Results demonstrated that men exhibited significantly (p < 0.05) greater relative force (M = 9.56 ± 1.25 N·kg−1, W = 8.15 ± 0.98) and relative power (M = 16.39 ± 4.22 W·kg−1, W = 9.98 ± 2.58) when compared to women. These findings demonstrate that men produce greater force and power than do women even relative to body weight when performing a simulated surfing pop-up movement. It appears that women may be at a disadvantage in regards to peak performance when compared to their male counterparts in the surfing pop-up movement. Therefore, women should train for both maximum and explosive upper-body strength in addition to their time spent surfing.

Effects of different elastic cord assistance levels on vertical jump.

Tran, TT, Brown, LE, Coburn, JW, Lynn, SK, Dabbs, NC, Schick, MK, Schick, EE, Khamoui, AV, Uribe, BP, and Noffal, GJ. Effects of different elastic cord assistance levels on vertical jump. J Strength Cond Res 25(12): 3472–3478, 2011—Currently, little research has been conducted using body weight reduction (BWR) as a means to enhance vertical jump. The purpose of this study was to determine the effects of different elastic cord assistance levels on vertical jump height (JH), takeoff velocity (TOV), relative ground reaction force (rGRF), relative impact force (RIF), and descent velocity (DV). Thirty recreationally trained college men and women (M = 15, W = 15) completed 3 testing sessions consisting of 5 conditions: 0, 10, 20, 30, and 40% BWR. In all BWR conditions, the subjects wore a full body harness while being attached to 2 elastic cords suspended from the ceiling and a linear velocity transducer. They then performed 3 maximal countermovement jumps with arm swing on a force plate. The results indicated no interaction of condition by sex for any variable; however, there was a significant (p < 0.05) main effect for condition for each variable. The JH significantly increased across all conditions (0%: 43.73 ± 1.62 cm, 40%: 64.77 ± 2.36 cm). The TOV at 30% (2.73 ± 0.34 m·s−1) was significantly greater than that at 0% (2.59 ± 0.39 m·s−1) and 10% (2.63 ± 0.34 m·s−1), whereas that at 40% (2.79 ± 0.43 m·s−1) was significantly greater than that at >0, 10, and 20%. The rGRF at 30% (18.62 ± 4.35 N·kg−1) was significantly greater than that at >0, 10, and 20%, whereas that at 40% (21.38 ± 5.21 N·kg−1) was significantly greater than in all conditions. The RIF at 20, 30, and 40% (40%: 61.60 ± 18.53 N·kg−1) was significantly greater than that at 0% (44.46 ± 9.12 N·kg−1). The DV at 20% (2.61 ± 0.31 m·s−1) was significantly greater than at 10%, whereas those at 30 and 40% (2.8 ± 0.41 m·s−1) were significantly greater than at 0, 10, and 20%. These results demonstrate that using different elastic cord levels to reduce body weight appears effective for increasing ascent and descent force and velocity variables. Future research should investigate greater BWR% and chronic training.