Jatin P. Ambegaonkar

Lower Body Stiffness and Muscle Activity Differences Between Female Dancers and Basketball Players During Drop Jumps

Background: Anterior cruciate ligament (ACL) injuries often occur during landing, with female athletes at higher injury risk than male athletes. Interestingly, female dancers have lower ACL injury rates than do female athletes in general. Hypothesis: Female dancers will have earlier and greater lower extremity muscle activity and higher sagittal knee joint and leg stiffness than will female basketball players. Study Design: Cross-sectional group comparison. Methods: Fifty-five healthy female athletes (35 dancers, 20 basketball players) performed 5 double-leg drop jumps from a 45-cm box. Surface electromyography (onsets and amplitudes; prelanding and postlanding) was recorded from the lateral gastrocnemius, medial and lateral hamstrings, lateral quadriceps muscles with a 3-dimensional electromagnetic tracking system, and forceplates recording biomechanics (leg spring stiffness and knee joint stiffness). Results: Compared with basketball players, dancers had greater leg spring stiffness (P = 0.047) but similar knee joint stiffness (P = 0.44). Although no significant differences were observed in overall muscle onset times (P = 0.22) or activation amplitudes (prelanding, P = 0.60; postlanding, P = 0.78), small to moderate effect sizes (ESs) suggest trends in dancers toward earlier (ES = 0.53) and higher medial hamstrings activation pre- (ES = 0.55) and post- (ES = 0.41) landing and lower lateral quadriceps (ES = 0.30) and higher gastrocnemius (ES = 0.33) postlanding muscle activation. Conclusions: In dancers, the higher leg spring stiffness and trends toward higher hamstrings prelanding and postlanding, as well as lower quadriceps and higher gastrocnemius activation postlanding with similar knee joint stiffness, indicate lower extremity neuromechanical differences across other joints. Clinical Relevance: Female dancers may have lower extremity neuromechanics that are different from those of basketball players during drop jumps. If dancers use ACL-protective strategies during activity, then their training routines should be further investigated to improve ACL injury prevention programs.

A Subsequent Movement Alters Lower Extremity Muscle Activity and Kinetics in Drop Jumps vs. Drop Landings

Ambegaonkar, JP, Shultz, SJ, and Perrin, DH. A subsequent movement alters lower extremity muscle activity and kinetics in drop jumps vs. drop landings. J Strength Cond Res 25(10): 2781–2788, 2011—Drop landings and drop jumps are common training exercises and injury research model tasks. Drop landings have a single landing, whereas drop jumps include a subsequent jump after initial landing. With the expected ground impact, instant and landing surface suggested to modulate landing neuromechanics, muscle activity, and kinetics should be the same in both tasks when landing from the same height onto the same surface. Although previous researchers have noted some differences between these tasks across separate studies, little research has compared these tasks in the same study. Thus, we examined whether a subsequent movement after initial landing alters muscle activity and kinetics between drop landings and jumps. Fifteen women performed 10 drop landings and drop jumps each from 45 cm. Muscle onsets and integrated muscle activation amplitudes 150 milliseconds before (preactivity) and after landing (postactivity) in the medial and lateral quadriceps, hamstrings, and lateral gastrocnemius and peak and time-to-peak vertical ground reaction forces were examined across tasks (p ≤ 0.05). When performing drop jumps, subjects demonstrated later (p = 0.02) gastrocnemius and lesser lateral gastrocnemius (p = 0.002) and medial quadriceps (p = 0.02) preactivity followed by increased postactivity in all muscles (p = 0.006), with higher peak vertical ground reaction forces (p = 0.04) but no differences in times to these peaks (p = 0.60) than drop landings. The later gastrocnemius activation, higher gastrocnemius and quadriceps postlanding amplitudes, and higher ground reaction forces in drop jumps may allow subjects to propel the body vertically after the initial landing vs. simply absorbing impact in drop landings. Our results indicate that in addition to landing surface and height, anticipation of a subsequent task changes landing neuromechanics. Generalizations of results from landing-only studies should not be made with landing followed-by-subsequent-activity studies. Landing exercises should be incorporated based on sport-specific demands.

State-Specific Differences in School Sports Preparticipation Physical Evaluation Policies

OBJECTIVE: This study evaluated the current preparticipation physical evaluation (PPE) administrative policies and cardiovascular screening content of all 50 states and Washington, DC. METHODS: PPE policies, documents, and forms from all 50 states and Washington, DC, were compared with the preparticipation physical evaluation–fourth edition (PPE-4) consensus recommendations. All electronic documents were publicly available and obtained from state interscholastic athletic associations. RESULTS: Fifty (98%) states required a PPE before participation. Most states (53%, n = 27) required a specific PPE form, whereas 24% (n = 12) of states recommended a specific form. Twenty-three states (45%) required or recommended use of the PPE-4 form or a modified version of it, and 27 states (53%) required or recommended use of outdated or unidentifiable forms. Ten states (20%) had not revised their PPE forms in >5 years. States permitted 9 different health care providers to administer PPEs. Only 22 states (43%) addressed all 12 of the PPE-4 personal and family history cardiovascular screening items, and 2 states (4%) addressed between 8 and 11 items. For the remaining 26 states, most (29%) addressed ≤3 screening items. CONCLUSIONS: Our results show that inconsistencies in PPE policies exist nationwide. Most states have been slow to adopt PPE-4 recommendations and do not adequately address the personal and family cardiovascular history questions. Findings suggest a need for PPE standardization nationwide and adoption of an electronic PPE process. This approach would enable creation of a national database and benefit the public by facilitating a more evidenced PPE.

Balance comparisons between female dancers and active nondancers.

Purpose: Female dancers have lower anterior cruciate ligament (ACL) injury rates compared with physically active women. Enhanced balance can decrease musculoskeletal injury risk. Dancers are proposed to have superior balance compared with physically active nondancers, and this may reduce their risk for ACL injury. However, whether female dancers actually have better balance than active nondancers is unclear. Method: Thirty-three women (15 dancers, 18 nondancers) performed the Balance Error Scoring System (BESS; error scores), the Star Excursion Balance Test (SEBT; percent leg length), and the Modified Bass Test of Dynamic Balance (BASS; maximum score = 100). Results: Dancers had fewer errors on the BESS than did nondancers (p < .001, 12.0 ± 6.9 vs. 25.3 ± 9.1). Dancers also had greater SEBT reach distances in the medial (right, p = .03, 90.4 ± 4.2% vs. 86.5 ± 5.5%; left, p = .04, 90.7 ± 4.5% vs. 86.7 ± 5.9%) and posteromedial directions (right, p = .01, 92.6 ± 5.6% vs. 87.0 ± 6.4%; left, p = .01, 93.9 ± 6.3% vs. 87.9 ± 6.3%), but not in the anteromedial direction (right, p = .23, 84.5 ± 4.4% vs. 86.2 ± 3.5%; left, p = .51, 86.4 ± 3.5% vs. 85.5 ± 4.0%). BASS scores were similar between groups (p = .58, 90.6 ± 5.5 vs. 91.7 ± 56). Conclusions: The novel findings of the study are that dancers had greater balance than did nondancers in some but not all tests. Although dancing may improve balance as compared with not dancing, it is not better than physical activity in improving balance. Thus, balance comparisons between dancers and nondancers may not fully explain why female dancers exhibit low ACL injury rates compared with physically active women. Other factors (e.g., anticipated/unanticipated movement demands) should be examined to understand the ACL injury disparity between dancers and physically active women.

Effects of unilateral and bilateral lower-body heavy resistance exercise on muscle activity and testosterone responses.

Abstract Jones, MT, Ambegaonkar, JP, Nindl, BC, Smith, JA, and Headley, SA. Effects of unilateral and bilateral lower-body heavy resistance exercise on muscle activity and testosterone responses. J Strength Cond Res 26(4): 1094–1100, 2012—Unilateral and bilateral lower-body heavy resistance exercises (HREs) are used for strength training. Little research has examined whether muscle activation and testosterone (TES) responses differ between these exercises. Our purpose was to compare the effects of unilateral and bilateral lower-body HRE on muscle activity using surface electromyography (sEMG) and TES concentrations. Ten resistance-trained, college-aged male athletes (football, track and field) completed 5 testing sessions in which bilateral (back squat [BS]) and unilateral (pitcher squat [PS]) exercises were performed using a counterbalanced design. Sessions 1 and 2 determined estimated maximum strength (10 repetition maximum [10RM]) in the BS and PS. During testing session 3, muscle activation (sEMG) was measured in the right vastus lateralis, biceps femoris, gluteus maximus, and erector spinae (ES) during both BS and PS (stance leg) exercises. In sessions 4 and 5, total TES concentrations (nanomoles per liter) were measured via blood draws at baseline (preexercise), 0, 5, 10, 15, and 30 minutes postexercise after 4 sets of 10 repetitions at the 10RM. Separate repeated-measures analyses of variance examined differences in sEMG and TES between BS and PS (p < 0.05). The sEMG amplitudes were similar (p = 0.80) for BS (0.22 ± 0.06 mV) and PS (0.20 ± 0.07 mV). The TES responses were also similar (p = 0.15) between BS (21.8 ± 6.9 nmol·L−1) and PS (26.2 ± 10.1 nmol·L−1). The similar lower limb and back sEMG and TES responses may indicate that the neuromuscular and hormonal demands were comparable for both the BS and PS exercises despite the absolute work being less in the PS. The PS exercise may be an effective method for including unilateral exercise into lower-body resistance training when designing training programs for ground-based activities.

Ankle Stabilizers Affect Agility but Not Vertical Jump or Dynamic Balance Performance

Ankle stabilizers can reduce ankle sprain incidence and severity by limiting range of motion. Still whether using them affects performance remains unclear. The authors compared effects of 3 ankle stabilizers, tape, lace-up (Swede-O Ankle Lok), and semirigid (Air-Cast Air-Stirrup) braces, and a nonsupport control on vertical jump (Sargent Jump Test), agility (Right-Boomerang Run test), and dynamic balance (Modified Bass Test) in 10 volunteers (4 males, 6 females; 25.6 ± 2.8 years, 167.8 ± 13.7 cm, 61.4 ± 10.7 kg) using repeated-measures ANOVAs. Participants had similar vertical jump (P = .27; control = 41.40 ± 11.89 cm, tape = 37.90 ± 7.92 cm, Swede-O = 41.40 ± 11.89 cm, Air-Cast = 39.29 ± 10.85 cm) and dynamic balance (P = .08; control = 92.50 ± 2.46, tape = 91.55 ± 3.53, Swede-O = 97.00 ± 5.32, Air-Cast = 89.40 ± 6.08) but differing agility scores (P = .03; control = 13.55 ± 1.35 seconds, tape = 14.03 ± 1.5 seconds, Swede-O = 14.10 ± 1.36 seconds, Air-Cast = 14.14 ± 1.41 seconds). Post hoc tests revealed a significant difference (P = .03) between control and Air-Cast but not between Swede-O (P = .06) or tape (P = .07). Effect size (d) analyses indicated that compared with control, all stabilizers trended to increase agility run times (tape, d = 0.33; Swede-O, d = 0.40; Air-Cast, d = 0.43). Since participants primarily required sagittal plane motion when jumping vertically and had relatively slow directional changes in the dynamic balance test, wearing ankle stabilizers did not hamper jump or balance. However, ankle stabilizers hindered participants’ ability to perform quick directional changes required in the agility test, with the most rigid stabilizer (Air-Cast) affecting agility the most. Clinicians should be aware that ankle stabilizers may affect some performance measures (agility) but not others (jumping, balance) and continue examinations in larger cohorts. Level of Evidence: Therapeutic, Level II

Changing Sagittal-Plane Landing Styles to Modulate Impact and Tibiofemoral Force Magnitude and Directions Relative to the Tibia

CONTEXT Ground reaction force (GRF) and tibiofemoral force magnitudes and directions have been shown to affect anterior cruciate ligament loading during landing. However, the kinematic and kinetic factors modifying these 2 forces during landing are unknown. OBJECTIVE To clarify the intersegmental kinematic and kinetic links underlying the alteration of the GRF and tibiofemoral force vectors secondary to changes in the sagittal-plane body position during single-legged landing. DESIGN Crossover study. SETTING Laboratory. PATIENTS OR OTHER PARTICIPANTS Twenty recreationally active participants (age = 23.4 ± 3.6 years, height = 171.0 ± 9.4 cm, mass = 73.3 ± 12.7 kg). INTERVENTION(S) Participants performed single-legged landings using 3 landing styles: self-selected landing (SSL), body leaning forward and landing on the toes (LFL), and body upright with flat-footed landing (URL). Three-dimensional kinetics and kinematics were recorded. MAIN OUTCOME MEASURE(S) Sagittal-plane tibial inclination and knee-flexion angles, GRF magnitude and inclination angles relative to the tibia, and proximal tibial forces at peak tibial axial forces. RESULTS The URL resulted in less time to peak tibial axial forces, smaller knee-flexion angles, and greater magnitude and a more anteriorly inclined GRF vector relative to the tibia than did the SSL. These changes led to the greatest peak tibial axial and anterior shear forces in the URL among the 3 landing styles. Conversely, the LFL resulted in longer time to peak tibial axial forces, greater knee-flexion angles, and reduced magnitude and a more posteriorly inclined GRF vector relative to the tibia than the SSL. These changes in LFL resulted in the lowest peak tibial axial and largest posterior shear forces among the 3 landing styles. CONCLUSIONS Sagittal-plane intersegmental kinematic and kinetic links strongly affected the magnitude and direction of GRF and tibiofemoral forces during the impact phase of single-legged landing. Therefore, improving sagittal-plane landing mechanics is important in reducing harmful magnitudes and directions of impact forces on the anterior cruciate ligament.

Fit to dance survey: a comparison with dancesport injuries.

The Fit to Dance survey has been conducted twice previously, in 1993 and 2002, without dancesport participants. The purpose of this present online survey was to supplement a comparison of dancesport against the earlier results. The current study had a greater percentage of male respondents than previous studies (43% vs 24% and 26%). The dancesport participants were older (28% at 40+ yrs vs 3% and 1%) and more likely to have normal (69% vs 57%) to overweight BMI (18% vs 2%). Dancesport participants spent more time in various non-dancing conditioning activities than previous surveys (5.2 ± 3.9 hrs SD vs 1.9 ± 2.5 and 2.2 ± 2.7). Muscles and joints were the most common type of injury in all the surveys. The knee was the top injury site in this survey, with lower back in previous surveys. The main perceived cause of injury was repetitive movements, whereas fatigue and overwork were cited in the previous surveys. Physiotherapists were the most common type of medical professionals from whom the dancers sought treatment for their injuries in all surveys. The first survey included recommendations that the present survey results agree with, including: dancers should be physically fit, dancers should warm up and cool down, dancers should never have to work in unsuitable environments, and dancers should receive immediate high-quality treatment for injuries.

Differences in pattern of variability for lower extremity kinematics between walking and running

This study characterizes walking and running patterns in healthy individuals using linear and nonlinear methods Seventeen individuals (12 males, 5 females) volunteered for the study. 3D kinematic data during walking (WA) and running (RU) on a motorized treadmill were captured using reflective markers placed on lower body (200Hz). A single 25s trial (5000 data points) was collected for each gait task. WA speed was 1.39±0.12m/s, whereas RU speed was 2.56±0.27m/s. Variables of interest included ankle plantar/dorsi flexion, knee flexion/extension, knee abduction/adduction, hip flexion/extension, and hip abduction/adduction angles. For linear analysis, standard deviation (SD) and coefficient of variation (CV) were calculated for the entire time series for both conditions. Nonlinear analysis included assessing pattern of regularity of respective kinematic time series using approximate entropy (ApEn). Inferential analyses were conducted using MANOVA to compare selected dependent measures (p<0.05). SD for knee flexion/extension angle (WA=23.34±4.17, RU=27.51±5.25) and ankle plantar/dorsi flexion angle (WA=9.24±2.37, RU=12.88±2.00) were both greater during running. For all other variables, there were no significant differences in degree of variability between walking and running (ps>0.05). Running ApEn values were greater than walking ApEn values for knee flexion/extension (WA=0.14±0.02, RU=0.23±0.04), knee abduction/adduction (WA=0.18±0.07, RU=0.24±0.07), hip flexion/extension (WA=0.09±0.02, RU=0.17±0.04), and hip abduction/adduction (WA=0.12±0.03, RU=0.21±0.05). Greater variability was demonstrated during running across all joints compared to walking. This suggests that ApEn is more sensitive to detecting changes between different gait conditions than standard discrete measures of variability (SD).

Changing filtering parameters affects lower extremity pre-landing muscle activation onset times

Surface electromyography(sEMG) is extensively used to examine muscle activation. Although raw sEMG signals are often filtered using Root-Mean-Square(RMS) algorithms, little agreement exists as to the time window over which signals should be processed. We examined the effects of differing RMS filtering windows on muscle onset times. Fifty-five participants performed 5 drop jumps from a 45 cm box and lateral gastrocnemius(LG), medial and lateral hamstring(MH, LH) and lateral quadriceps(LQ) muscle activity were acquired. Signals were collected at 1000 Hz and RMS filtered using 3 ms, 10 ms, 20 ms and 25 ms windows. Muscle onset times differed by RMS windows for the LG(p= 0.01), MH(p= 0.002), and LH(p= 0.000), but not for the LQ(p=0.14). Pairwise comparisons indicated that LG onsets were earlier with the 3 ms vs. 20 ms window, MH onsets were earlier with the 3 ms vs. 20 ms and 25 ms windows, and LH onsets were earlier with the 3 ms, 10 ms, and 20 ms windows than the 25 ms window. Gastrocnemius and hamstring muscle onset times were substantially earlier when filtering raw sEMG data with 3 ms versus wider RMS windows(> 20 ms) during landing. Changing filtering parameters affects data interpretation when analyzing sEMG data using differing window widths. Additional research should determine optimal RMS window widths that maximize signal fidelity but still retain meaningful time differences.