Muscle activation during single leg squat is affected by position of the nonstance limb

ABSTRACT Context: The single leg squat (SLS) is appropriate for targeting activation, strengthening, and/or neuromuscular retraining of the gluteus maximus, gluteus medius, and quadriceps. However, the effect of different non-stance leg positions on muscle activity has not been fully evaluated. Objective: To compare the muscle activity of selected stance leg hip muscles during the SLS with 3 non-stance leg positions: in front, in the middle, and in back. Design: Controlled laboratory study. Setting: Biomechanics laboratory. Participants: Seventeen healthy adults. Main Outcome Measure(s): Surface EMG data of the gluteus maximus, gluteus medius, lateral hamstrings, medial hamstrings, rectus femoris, and TFL as well as kinetic data of the hip and knee were collected while participants performed the 3 SLS tasks. Mean muscle activation levels during the descent phase and ascent phase for the selected hip muscles were compared for the 3 tasks. Hip and knee kinetics in all 3 planes were also compared for the 3 tasks. Each variable of interest was analyzed using a separate linear regression model with a generalized estimating equations correction. Results: Muscle activation levels of the gluteus maximus, gluteus medius, medial hamstrings, rectus femoris, and TFL on the stance leg during descent, and the medial hamstrings and TFL during ascent were significantly different between SLS tasks. The greatest number of differences occurred between SLS-Front and SLS-Back. During descent, gluteal muscle activity was greater in SLS-Front and SLS-Middle than in SLS-Back. For both phases, TFL activity was greater during SLS-Front than both SLS-Middle and SLS-Back. Kinetic differences at the hip and knee between SLS tasks were also observed. Conclusion: The 3 SLS tasks have different muscle activation and kinetic profiles. Clinician and researchers can vary non-stance leg position during the SLS to manipulate muscle activation levels and tailor the exercise to assist with goals at different stages of rehabilitation.

KEY ENGINEERING SOLUTIONS IMPLEMENTED IN ROCKET AND SPACE SYSTEM VOSTOK TO ASSURE CREW SAFETY DURING ASCENT (towards 60th anniversary of the first man in space)

The paper analyzes engineering and operational solutions implemented in rocket and space system Vostok to assure crew safety during ascent in view of the need to complete the work on an extremely short notice. It reviews the results of flight tests of launch vehicles belonging to the R7 family and the status of during prelaunch processing and ascent phase. The paper draws comparisons between work to develop a crew escape system by the time when the first manned mission of Vostok spacecraft took place. It provides an analysis of emergencies and measures to assure safety our country’s project Vostok and US project Mercury. Key words: rocket and space system, spacecraft, descent vehicle, crew safety.

KEY ENGINEERING SOLUTIONS IMPLEMENTED IN ROCKET AND SPACE SYSTEM VOSTOK TO ASSURE CREW SAFETY DURING ASCENT (towards 60th anniversary of the first man in space)

The paper analyzes engineering and operational solutions implemented in rocket and space system Vostok to assure crew safety during ascent in view of the need to complete the work on an extremely short notice. It reviews the results of flight tests of launch vehicles belonging to the R7 family and the status of work to develop a crew escape system by the time when the first manned mission of Vostok spacecraft took place. It provides an analysis of emergencies and measures to assure safety during prelaunch processing and ascent phase. The paper draws comparisons between our country’s project Vostok and US project Mercury. Key words: rocket and space system, spacecraft, descent vehicle, crew safety.

Attitude Control in Ascent Phase of Missile Considering Actuator Non-Linearity and Wind Disturbance

During the ascent phase of a missile, a challenging problem occurs that blocks the construction of a high-precision attitude control scheme, which directly affects accurate modeling including disturbances: non-linearities of an actuator, rapidly time-varying parameters, un-modeled dynamics, etc. In order to improve the control performance, an active disturbance rejection control (ADRC) scheme, considering non-linear dynamics of the actuator and wind disturbance during the ascent phase, is proposed in this paper. An expand state observer (ESO) is planned to estimate and compensate the actuator’s non-linear dynamics, flight model uncertainties, and wind disturbance. Therefore, the complex non-linear time-varying control problem is simplified into a linear time-invariant control problem. The pitch attitude control system is controlled by the cascade method and ADRC controllers are designed for actuator close loop and attitude control loop, respectively. The simulation results show that ADRC has strong robustness under different dead-zones and external disturbances of the actuator. On the other hand, ADRC can effectively suppress the external atmospheric disturbance. Compared with the traditional gain-scheduling control scheme, the ADRC scheme can significantly reduce the overloading of the system and shows remarkable performance for tracking as well as wind resistance.