RESUMO
Background: Weightlifting is growing in popularity among recreational and competitive athletes. The barbell back squat (BackS) is commonly included in these training programs, while the barbell front squat (FrontS) is commonly performed as a component of other lifts such as the power clean or clean and jerk, it is less commonly practiced in isolation. Hypothesis/Purpose: The purpose of this study was to examine the effects of VPAC performance on trunk muscle and LE biomechanical responses during loaded BackS versus FrontS in healthy subjects. Study Design: Controlled Laboratory Study. Methods: Healthy male subjects with the ability to perform a sub-maximal loaded barbell squat lift were recruited. Subjects completed informed consent, demographic/medical history questionnaires and an instructional video. Subjects practiced VPAC and received feedback. Surface electromyography (sEMG) electrodes and kinematic markers were applied. Muscles included were the internal oblique (IO), external oblique (EO), rectus abdominis, iliocostalis lumborum (ICL), superficial multifidi, rectus femoris, vastus lateralis, biceps femoris, and gluteus maximus. Maximal voluntary isometric contractions established reference sEMG values. A squat one-rep-max (1RM) was predicted by researchers using a three to five repetition maximum (3RM, 5RM) load protocol. Subjects performed BackS trials at 75% 1RM while FrontS trials were performed at 75% BackS weight, both with and without VPAC. Subjects performed three repetitions of each condition with feet positioned on two adjacent force plates. Significant interactions and main effects were tested using a 2(VPAC strategy) x 2(squat variation) and 2(VPAC strategy) x 2(direction) within-subject repeated measures ANOVAs. Tukey's Post-Hoc tests identified the location of significant differences. Results: Trunk muscle activity was significantly higher during FrontS versus BackS regardless of VPAC condition. (IO: p=0.018, EO: p<0.001, ICL: p<0.001) VPAC increased performance time for both squat variations (p=.0011), which may be associated with decreased detrimental force potential on the lumbar spine and knees. VPAC led to improved ability to maintain a neutral lumbar spine during both squat variations. This finding is associated with decreased detrimental force potential on the lumbar spine. Conclusions: Findings could help guide practitioners and coaches to choose squat variations and incorporate VPAC strategies during their treatments and/or training programs. Level of Evidence: Level 3©The Author(s).
RESUMO
CASE DESCRIPTION: A 30-year-old person with a unilateral transtibial amputation (TTAmp) was assessed performing an Olympic-style back squat with an energy storage and return prosthetic foot. OBJECTIVE: Determine joint-level movement strategies of an individual with TTAmp while performing an Olympic-style back squat. STUDY DESIGN: Case study design. TREATMENT: Back squat mechanics are evaluated in an individual with TTAmp by comparing the contribution of the ankle, knee, and hip joint to total positive and negative amputated and sound limb work. OUTCOMES: The hip joint was the greatest contributor to total positive limb work compared with the knee and ankle, respectively, in the amputated (55.0% hip vs. 30.8% knee, P < 0.001; vs. 14.2% ankle, P = 0.001) and sound limbs (52.2% hip vs. 38.9% knee, P < 0.001; vs. 8.9% ankle, P < 0.001). The hip joint was the greatest contributor to total negative limb work compared with the ankle in both the amputated (51.0% hip vs. 15.9% ankle, P < 0.001) and sound limbs (47.3% hip vs. 10.0% ankle, P < 0.001) and the knee in the amputated limb (51.0% hip vs. 32.5% knee, P < 0.001). Ankle joint power demonstrated an atypical bimodal negative/positive/negative/positive pattern. CONCLUSION: The individual with TTAmp used a hip-dominant joint strategy in both the amputated and sound limbs while demonstrating more potential to optimize the prosthetic foot's energy storage and return capabilities when performing a back squat.