John W Whitting

Dorsiflexion capacity affects achilles tendon loading during drop landings

PURPOSE Evidence suggests a link between decreased dorsiflexion range of motion (DROM) and injury risk during landings. The purpose of this study was to determine the effect of weight-bearing DROM on ankle mechanics during drop landings. METHODS Forty-eight men (mean ± SD = 22.5 ± 4.7 yr) were measured for DROM. Participants performed drop landings onto a force platform at two vertical descent velocities (2.25 ± 0.15 and 3.21 ± 0.17 m·s(-1)), while EMG activity of four shank muscles and three-dimensional ankle joint kinematics were recorded. Participants were classified into low (37.7° ± 2.5°) and high (48.4° ± 2.5°) DROM groups. RESULTS Ground reaction force, EMG, dorsiflexion angle, plantarflexion moment, and Achilles tendon force outcome variables were all equivalent for the two DROM groups during each landing condition. However, the low DROM group performed each landing condition at a significantly greater percentage of their DROM and displayed significantly more ankle eversion throughout most of the movement. The low and high DROM groups displayed DROM percentages of 27 ± 11 and 10 ± 11 (P = 0.013), 32 ± 9 and 23 ± 9 (P = 0.056), 60 ± 13 and 46 ± 13 (P = 0.004), and 66 ± 16 and 54 ± 9 (P = 0.003) when they encountered the peak plantarflexion moments, Achilles tendon force, eversion angles, and dorsiflexion angles, respectively. CONCLUSION Participants with a low DROM absorbed the landing impact forces with their plantarflexor muscle-tendon units in a more lengthened and everted position. Athletes with a low DROM may be more likely to regularly overload their plantarflexor muscle-tendon units, thereby potentially exposing themselves to a higher likelihood of incurring injuries such as Achilles tendinopathy.

Parachute landing fall characteristics at three realistic vertical descent velocities

INTRODUCTION Although parachute landing injuries are thought to be due in part to a lack of exposure of trainees to realistic descent velocities during parachute landing fall (PLF) training, no research has systematically investigated whether PLF technique is affected by different vertical descent conditions, with standardized and realistic conditions of horizontal drift. This study was designed to determine the effects of variations in vertical descent velocity on PLF technique. METHODS Kinematic, ground reaction force, and electromyographic data were collected and analyzed for 20 paratroopers while they performed parachute landings, using a custom-designed monorail apparatus, with a constant horizontal drift velocity (2.3 m x s(-1)) and at three realistic vertical descent velocities: slow (2.1 m x s(-1)), medium (3.3 m x s(-1)), and fast (4.6 m x s(-1)). RESULTS Most biomechanical variables characterizing PLF technique were significantly affected by descent velocity. For example, at the fast velocity, the subjects impacted the ground with 123 degrees of plantar flexion and generated ground reaction forces averaging 13.7 times body weight, compared to 106 degrees and 6.1 body weight, respectively, at the slow velocity. Furthermore, the subjects activated their antigravity extensor muscles earlier during the fast velocity condition to eccentrically control the impact absorption. DISCUSSION As vertical descent rates increased, the paratroopers displayed a significantly different strategy when performing the PLF. It is therefore recommended that PLF training programs include ground training activities with realistic vertical descent velocities to better prepare trainees to withstand the impact forces associated with initial aerial descents onto the Drop Zone and, ultimately, minimize the potential for injury.

Passive dorsiflexion stiffness is poorly correlated with passive dorsiflexion range of motion

OBJECTIVES The purpose of this study was to determine the relationships among passive measures of weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness, thereby establishing whether they assess similar mechanical characteristics, as each measure has been implicated in injury risk during landings. DESIGN Cross-sectional study. METHODS Passive weight-bearing dorsiflexion range of motion, non-weight-bearing dorsiflexion range of motion and dorsiflexion stiffness were quantified for 42 males (22.8±5.0 years). The relationship between each data set was calculated using Pearson product-moment correlation coefficients. RESULTS Although weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were significantly correlated, the strength of the relationship was poor (r(2)=0.18; p=0.004). Weight-bearing dorsiflexion range of motion (mean=43.0±5.0°) was significantly greater than non-weight-bearing dorsiflexion range of motion (29.8±5.9°; p<0.001) and weight-bearing dorsiflexion range of motion and non-weight-bearing dorsiflexion range of motion were also poorly correlated with passive dorsiflexion stiffness (1.48±0.55Nm°(-1); r(2)=0.04 and r(2)=0.14, respectively), despite the latter relationship being significant (p=0.017). CONCLUSIONS Passive dorsiflexion stiffness was not strongly associated with dorsiflexion range of motion, despite the significant correlation in the non-weight-bearing condition. It must be acknowledged that passive dorsiflexion stiffness was weakly associated with dorsiflexion range of motion, although the strength of the association suggests that it may not necessarily determine dorsiflexion range of motion. Furthermore, the functional dorsiflexion limits of the ankle during weight-bearing tasks may be underestimated or misrepresented by non-weight-bearing measures of dorsiflexion range of motion. Therefore, although ankle dorsiflexion range of motion and dorsiflexion stiffness have been implicated in injury risk during weight-bearing tasks such as landings, it may be due to different mechanisms.

Does Foot Pitch at Ground Contact Affect Parachute Landing Technique

The Australian Defence Force Parachute Training School instructs trainees to make initial ground contact using a flat foot whereas United States paratroopers are taught to contact the ground with the ball of the foot first. This study aimed to determine whether differences in foot pitch affected parachute landing technique. Kinematic, ground reaction force and electromyographic data were analyzed for 28 parachutists who performed parachute landings (vertical descent velocity = 3.4 m x s(-1)) from a monorail apparatus. Independent t-tests were used to determine significant (p < 0.05) differences between variables characterizing foot pitch. Subjects who landed flat-footed displayed less knee and ankle flexion, sustained higher peak ground reaction forces, and took less time to reach peak force than those who landed on the balls of their feet. Although forefoot landings lowered ground reaction forces compared to landing flat-footed, further research is required to confirm whether this is a safer parachute landing strategy.

Influence of footwear type on barbell back squat using 50, 70 and 90% of one repetition maximum: a biomechanical analysis

Abstract Whitting, JW, Meir, RA, Crowley-McHattan, ZJ, and Holding, RC. Influence of footwear type on barbell back squat using 50, 70, and 90% of one repetition maximum: a biomechanical analysis. J Strength Cond Res 30(4): 1085–1092, 2016—The effect of footwear type was investigated during the barbell back squat using three-dimensional motion analysis and ground reaction force data. Nine male participants (mean age = 26.4 ± 5.4 years, height = 1.79 ± 0.08 m, and mass = 84.7 ± 16.1 kg) completed 2 experimental testing sessions wearing 2 different forms of training footwear: (a) standard sports trainers (running shoes [RS]) and (b) specialized weightlifting shoes (WS). On each test day, participants completed a sequence of 5, 3, and 1 repetitions of a barbell back squat using 50, 70, and 90%, respectively, of their 1 repetition maximum (1RM) load in each of the shoe conditions. Shoe order, which was initially randomly assigned for test day 1, was reversed on test day 2. Significant main effects were found for peak dorsiflexion of both left (p < 0.001) and right (p < 0.001) ankles. Pairwise post hoc comparisons showed that the RS condition exhibited significantly more dorsiflexion compared with the WS condition in both left and right ankles. There was also a significant main effect of load (%1RM) within the left ankle (p < 0.01) with post hoc comparisons showing that there was a significant increase in peak dorsiflexion angle from 50 to 90% (p ⩽ 0.05) and 70–90% of 1RM (p ⩽ 0.05) but no difference between 50 and 70% of 1RM (p = 1.000). These findings indicate that further investigation is necessary to substantiate claims regarding the benefits of wearing WS during resistance training exercises targeting the squat movement.

Monopolar electromyographic signals recorded by a current amplifier in air and under water without insulation

It was recently proposed that one could use signal current instead of voltage to collect surface electromyography (EMG). With EMG-current, the electrodes remain at the ground potential, thereby eliminating lateral currents. The purpose of this study was to determine whether EMG-currents can be recorded in Tap and Salt water, as well as in air, without electrically shielding the electrodes. It was hypothesized that signals would display consistent information between experimental conditions regarding muscle responses to changes in contraction effort. EMG-currents were recorded from the flexor digitorum muscles as participants squeezed a pre-inflated blood pressure cuff bladder in each experimental condition at standardized efforts. EMG-current measurements performed underwater showed no loss of signal amplitude when compared to measurements made in air, although some differences in amplitude and spectral components were observed between conditions. However, signal amplitudes and frequencies displayed consistent behavior across contraction effort levels, irrespective of the experimental condition. This new method demonstrates that information regarding muscle activity is comparable between wet and dry conditions when using EMG-current. Considering the difficulties imposed by the need to waterproof traditional bipolar EMG electrodes when underwater, this new methodology is tremendously promising for assessments of muscular function in aquatic environments.

Effects of passive ankle dorsiflexion stiffness on ankle mechanics during drop landings.

OBJECTIVES Vertical landing tasks strain the Achilles tendon and plantar-flexors, increasing acute and overuse strain injury risk. This study aimed to determine how passive ankle dorsiflexion stiffness affected ankle mechanics during single limb drop landings at different vertical descent velocities. DESIGN Cross-sectional study. METHODS Passive ankle dorsiflexion stiffness and passive weight-bearing dorsiflexion range of motion (DROM) were quantified for 42 men. Participants were then grouped as having low (LPS: 0.94±0.15 Nm°⁻¹; n=16) or high (HPS: 2.05±0.36 Nm°⁻¹; n=16; p<0.001) passive ankle dorsiflexion stiffness. Three-dimensional ankle joint kinematics was quantified while participants performed drop landings onto a force platform at two vertical descent velocities (slow: 2.25±0.16 ms⁻¹; fast: 3.21±0.17 ms⁻¹). RESULTS Although affected by landing velocity, there were no significant effects of passive ankle dorsiflexion stiffness, nor any significant ankle dorsiflexion stiffness×vertical descent velocity interactions on any outcome variables characterising ankle mechanics during drop landings. Furthermore, there was no significant difference between the groups for passive weight-bearing DROM (LPS: 43.9±4.1°; HPS: 42.5±5.7°), indicating that the results were not confounded by between-group differences in ankle range of motion. CONCLUSIONS Neither high nor low passive ankle dorsiflexion stiffness was found to influence ankle biomechanics during drop landings at different descent velocities. Landing strategies were moderated more by the demands of the task than by passive ankle dorsiflexion stiffness, indicating that passive ankle dorsiflexion stiffness may not affect plantar-flexor strain during a drop landing.

Scoring Analysis of Manoeuvres Performed in Elite Male Professional Surfing Competitions

PURPOSE To investigate the influence of turns, tube rides, and aerial maneuvers on the scores awarded in elite mens professional surfing competitions. The successful completion rate and scores associated with different aerial variations were also investigated. METHODS Video recordings from all 11 events of the 2015 World Surf League mens world championship tour were viewed to classify maneuvers performed by the competitors on each wave as turns, tube rides, and aerials. A 2-way ANOVA was used to determine any main effect or interaction of maneuver type or event location on the wave scores. A 1-way ANOVA was used to determine any main effect of aerial type on successful completion rate. RESULTS Aerial maneuvers were scored significantly higher than tube rides and turns. A significant main effect existed for maneuver and completion rate. Aerial maneuvers had the lowest completion rate, 45.4%. During the finals series (quarterfinals, semifinals, and finals heats) aerial-maneuver completion rate was higher, 55.4%. The frontside air reverse was the most commonly performed maneuver and received an average score of 6.77 out of 10. CONCLUSION Professional surfers can optimize their potential single-wave scores during competition by successfully completing aerial maneuvers. However, aerial maneuvers continue to be a high-risk maneuver with a significantly lower completion rate. Our findings suggest that surfers should aim to improve their aerial-maneuver completion rate via surf practice or land-based training drills.

Preventing injuries associated with military static-line parachuting landings

Military static-line parachuting is a highly tactical and hazardous activity, with a well-documented injury risk. Due to the high impact forces and rapid rate of loading when a parachutist lands, injuries most frequently occur to the lower limbs and the trunk/spine, with ankle injuries accounting for between 30 and 60 % of all parachuting injuries. Although military static-line parachuting injuries can be sustained at any time between the paratrooper attempting to leave the aircraft until they have landed and removed their harness, most injuries occur on landing. Throughout the world, various landing techniques are taught to paratroopers to reduce the risk of injury, by enabling parachute landing forces to be more evenly distributed over the body. In this chapter, we review research associated with static-line military parachuting injuries, focusing on injuries that occur during high-impact landings. We summarize literature pertaining to strategies for military paratroopers to land safely upon ground contact, especially when performing the parachute fall landing technique. Recommendations for future research in this field are provided, particularly in relation to the parachute fall landing technique and training methods. Ultimately, any changes to current practice in landing technique, how it is taught, and whether protective equipment is introduced, should be monitored in well controlled, prospective studies, with the statistical design accounting for the interaction between the variables, to determine the effect of these factors on injury rates and paratrooper performance. This will ensure that evidence-based guidelines can be developed, particularly in relation to landing technique and how this is trained, in order to minimize injuries associated with landings during military static-line parachuting in subsequent training and tactical operations.This book provides a state-of-the-art update, as well as perspectives on future directions of research and clinical applications in the implementation of biomechanical and biophysical experimental, theoretical and computational models which are relevant to military medicine. Such experimental and modeling efforts are helpful, on the one hand, in understanding the aetiology, pathophysiology and dynamics of injury development and on the other hand in guiding the development of better equipment and protective gear or devices that should ultimately reduce the prevalence and incidence of injuries or lessen their hazardous effects. The book is useful for military-oriented biomedical engineers and medical physicists, as well as for military physiologists and other medical specialists who are interested in the science and technology implemented in modern investigations of military related injuries

Understanding successful and unsuccessful landings of aerial maneuver variations in professional surfing

Although performing aerial maneuvers can increase wave score and winning potential in competitive surfing, the critical features underlying successful aerial performance have not been systematically investigated. This study aimed to analyze highly skilled aerial maneuver performance and to identify the critical features associated with successful or unsuccessful landing. Using video recordings of the World Surf Leagues Championship Tour, every aerial performed during the quarterfinal, semifinal, and final heats from the 11 events in the 2015 season was viewed. From this, 121 aerials were identified with the Frontside Air (n = 15) and Frontside Air Reverse (n = 67) being selected to be qualitatively assessed. Using chi‐squared analyses, a series of key critical features, including landing over the center of the surfboard (FS Air χ2 = 14.00, FS Air Reverse χ2 = 26.61; P < .001) and landing with the lead ankle in dorsiflexion (FS Air χ2 = 3.90, FS Air Reverse χ2 = 13.64; P < .05), were found to be associated with successful landings. These critical features help surfers land in a stable position, while maintaining contact with the surfboard. The results of this study provide coaches with evidence to adjust the technique of their athletes to improve their winning potential.