Stable to unstable differences in force-velocity-power profiling during chest presses and squats

Biomechanical analysis of lifting on stable versus unstable surfaces-a laboratory-based proof-of-concept study

Background

Many workers performing manual handling tasks suffer from musculoskeletal disorders (MSD). Previous research has identified several loading aspects associated with manual handling, but it is still unknown if lifting on an unstable surface is associated with increased biomechanical loading of different body parts.

Aim

This proof-of-concept study aims to study what kinematic and kinetic movement parameters, such as movement time, joint angles, torque, and muscle activity are feasible and of importance when studying the effect of lifting on surfaces with varying degrees of stability in an experimental set-up.

Methods

Measurements were taken during three different surface conditions: stable, slightly unstable, and unstable. The participants were instructed to lift a box from the floor and place it on a table in front of them. The weight of the box varied from 0.5 to 15.5 kg. By using a motion capture system (VICON) with 28 reflective markers placed on the participants and one on the box, one Kistler force plate for measuring force levels and center of pressure movements (CoP), and four electromyographic transmitters (EMG), we analyzed the downward and upward phases of the lifting movement, using the Friedman’s test for repeated measures.

Results

Statistically significant results with less joint movements in the lower and upper back were seen with increased instability during both the downward and upward phases. The decrease in trunk movements with increased instability resulted in a somewhat more flexed knee position during the movement, a lower torque in the lower back, and a decrease in CoP movements, but no differences in movement time or muscle activity in back and knee muscles.

Conclusion

Lifting while standing on unstable surfaces resulted in an alteration of both kinematics and kinetics parameters; however, further studies regarding whether this is an additional risk factor for developing lower back pain are needed. Muscle activity levels were not altered due to instability and due to the complexity of the measurement, and we suggest not including EMG measures in future experiments of this type.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40814-022-01157-2.

Effects of Verbal Encouragement and Performance Feedback on Physical Fitness in Young Adults

This study evaluates the effects on the performance of young adults undergoing physical fitness tests with external stimuli (verbal encouragement (VE), performance feedback (PF), goal-oriented (GO) and a combination of external stimuli (CS)) and without external stimuli (WS). A group of 432 male students (age 19.1 ± 2.1 y, BMI 24.72 ± 5.97) was randomly selected for this study. They underwent a battery of fitness tests (bench press, 10 and 30 m sprints, and vertical jump) with and without external stimuli. The results showed greater improvements in mean power in bench press after PF compared to attempts WS (14.93 W, 3.43%, p = 0.005), and after CS compared to WS (13.84 W, 3.18%, p = 0.015). The time in the 10 and 30 m sprints decreased more profoundly after a combination of VE and GO compared to WS (0.021 s, 1.07%, p = 0.000 and 0.06 s, 1.23%, p = 0.001, respectively) and after CS compared to VE (0.015 s, 0.76%, p = 0.004 and 0.074 s, 1.52%, p = 0.000, respectively). Furthermore, the height of the jump improved more after VE than WS (1.36 cm, 5.46%, p = 0.000), after CS than WS (1.94 cm, 7.79%, p = 0.000), and after CS than VE stimulus (0.58 cm, 2.21%, p = 0.000). These findings indicate that external stimuli and their combination are more effective for achieving better results in physical fitness tests than without external stimuli. Therefore, practitioners should use verbal encouragement, performance feedback, goal-oriented stimuli, and their combinations during physical fitness testing in physical education classes in order to enable their students to achieve a better performance.