Parachutes, randomized controlled trials, and all-cause mortality.

In 2003 and 2018 researchers discussed the perils of blind reliance on randomized controlled trials that have been substituted for medical experience and clinical acumen. Although these past articles do well to shed light on this issue, they neglect to discuss the topic of all-cause mortality in controlled trials. The current essay seeks to fill this void and expand the thought put into the appropriateness of all-cause mortality, especially when trials extend excessively far into the future. To do this effectively the current essay leans on trial data from statin research and evidence from cancer screening-where researchers have explicitly called for all-cause mortality to be used in lieu of cancer or cardiovascular specific mortality. The issue with such an endpoint is that it obfuscates the issue at hand, namely that a specific intervention is intended to have a specific effect, not that a specific intervention is supposed to have any kind of effect. The effect(s) of medical interventions ought to be relevant to their intended mechanism of action and not simply any positive effect that can be pulled from trial data.

Risk Factors for Injuries During Military Static-Line Airborne Operations: A Systematic Review and Meta-Analysis.

OBJECTIVE: To identify and analyze articles in which the authors examined risk factors for soldiers during military static-line airborne operations. DATA SOURCES: We searched for articles in PubMed, the Defense Technical Information Center, reference lists, and other sources using the key words airborne, parachuting, parachutes, paratrooper, injuries, wounds, trauma, and musculoskeletal. STUDY SELECTION: The search identified 17 684 potential studies. Studies were included if they were written in English, involved military static-line parachute operations, recorded injuries directly from events on the landing zone or from safety or medical records, and provided data for quantitative assessment of injury risk factors. A total of 23 studies met the review criteria, and 15 were included in the meta-analysis. DATA EXTRACTION: The summary statistic obtained for each risk factor was the risk ratio, which was the ratio of the injury risk in 1 group to that of another (baseline) group. Where data were sufficient, meta-analyses were performed and heterogeneity and publication bias were assessed. DATA SYNTHESIS: Risk factors for static-line parachuting injuries included night jumps, jumps with extra equipment, higher wind speeds, higher air temperatures, jumps from fixed-wing aircraft rather than balloons or helicopters, jumps onto certain types of terrain, being a female paratrooper, greater body weight, not using the parachute ankle brace, smaller parachute canopies, simultaneous exits from both sides of an aircraft, higher heat index, winds from the rear of the aircraft on exit entanglements, less experience with a particular parachute system, being an enlisted soldier rather than an officer, and jumps involving a greater number of paratroopers. CONCLUSIONS: We analyzed and summarized factors that increased the injury risk for soldiers during military static-line parachute operations. Understanding and considering these factors in risk evaluations may reduce the likelihood of injury during parachuting.

Experimental study on the half-squat parachute landing for driving and validating the inverse dynamic simulation / 医用生物力学

Objective To provide data for establishing, driving and validating the inverse dynamics model of AnyBody Modeling System, the simulated half squat parachute landing experiment was designed and relevant data were collected. Method The subject was required to jump from a 0.32 m high platform to simulate the half squat parachute landing. The kinematic parameter of lower extremity joint, the ground reaction force and the surface electromyogram (SEMG) of four main muscles in the lower extremity joint were measured simultaneously. Results The angle changes of hip, knee and ankle along with time in three anatomical planes, the ground reaction force of right foot and the trajectory of the center of pressure were collected within 1 second just before and after the subject landing. These data would be used to drive the muscleskeletal model, while the data for measuring electromyogram activity would be used to validate the model. Conclusions The experiment meets the requirement of muscleskeletal model analysis, which can be used for further study of half squat parachute landing.

Finite element study on knee injuries in the parachute landing / 医用生物力学

Objective To numerically simulate the half squat parachute landing and analyze the mechanism of knee injuries with the finite element method based on the data of the simulated parachute landing experiment. Method The half squat parachuting experiment was performed by 16 healthy volunteers. The heights of simulated landing were 0.32 m, 0.52 m and 0.72 m respectively. A three dimensional finite element model of human knee joint was developed based on magnetic resonance images. The kinematical data of the knee and the data of the reaction force obtained by experiments were used to make a numerical simulation of the parachute landing process. Results The stress level of the knee increased with the increase of the height. The lateral meniscus and cartilage suffered greater loads than the medial ones. Obvious stress concentrations occurred in the anterior cruciate ligament and the medial collateral ligament when the knee flexion degree reached the peak value. Conclusions The severe impact in parachute landing is the direct cause of injuries in parachute landing. The lateral cartilage and meniscus are more likely to be injured, and the anterior cruciate ligament and the medial collateral ligament are easier to tear when the knee flexion degree reaches the peak value.

Effects of ankle stabilizers on electromyographic activities of lower extremity muscles during simulated half-squat parachute landing / 医用生物力学

Objective To study effects of ankle stabilizer on electromyographic activities of lower extremity muscles during the simulated half squat parachute landing and its gender differences. Method Eight male and eight female healthy adults were required to jump from a platform of 0.72 m high to simulate half squat parachute landing. The experiment was divided into 3 groups: the barefoot one as control group, the group wearing tapes and braces respectively. The electromyogram (EMG) of each subject’s tibial anterior, lateral gastrocnemius, biceps femoralis and rectus femoralis was measured. Two way ANOVA was used to analyze and evaluate the effect of the stabilizers and genders on EMG variables. Results The use of brace significantly increased the pre landing EMG amplitude of the tibialis anterior for male (Control: 266 μV; Tape: 368 μV; Brace: 552 μV). The stabilizers had no significant effects on the other EMG parameters. Conclusions Semi rigid ankle braces are capable of arousing more active EMG of male’s ankle flexor during half squat parachute landing, but female does not share this predominance. Ankle stabilizers have no significant effects on EMG activities for knee joints.