A BIOMECHANICAL ANALYSIS OF FRONT VERSUS BACK SQUAT: INJURY IMPLICATIONS

The aim of this study was to examine the differences in trunk and lower limb kinematics between the front and back squat. 2D kinematic data was collected as participants (n = 12) completed three repetitions of both front and back squat exercises at 50 % of their back squat one repetition maximum. Stance width was standardised at 107(±10) % of biacromial breadth. The Wilcoxon signed ranks test was used to examine significant differences in dependent variables between both techniques. Results showed that the back squat exhibited a significantly greater trunk lean than the front squat throughout (p < 0.05) with no differences occurring in knee joint kinematics. The results of this study in conjunction with other squat related literature (Russell et al., 1989) suggest that the back squat gives rise to an increased risk of lower back injury

A BIOMECHANICAL COMPARISON OF THE BACK SQUAT AND HEXAGONAL BARBELL DEADLIFT

Cody A. Stahl1, Eoghan M.P. Trihy2, David Diggin2, Deborah L. King2 1School of Kinesiology Applied Health and Recreation, Oklahoma State University, Stillwater, Oklahoma; 2Department of Exercise and Sport Sciences, Biomechanics Laboratory, Ithaca College, Ithaca, New York. Exercises such as the back squat (BS) and conventional deadlift (CDL) are used interchangeably by strength and conditioning coaches to improve athletes’ lower body strength. More recently, the hexagonal barbell deadlift (HBD) has been used as an auxiliary exercise for the CDL and BS. Anecdotally, the HBD encourages amore upright trunk position which can reduce compressive and shear loads on the spine relative to the CDL and BS. PURPOSE: This study examined differences in kinematics and kinetics between BS and HBD exercises during 1RM testing. METHODS: 16 participants volunteered for the study (6 males, 10 females; age 21.4 ± 3.0 years; height 169.7 ± 6.5 cm; mass 73.8 ± 10.9 kg). Participants attended the lab on 2 occasions spaced 7 days apart. Participants underwent 1RM testing of either the BS or HBD during each session. Following a warm-up, participants attempted to achieve their 1RM within 3–5 attempts. Kinematic and kinetic data were collected using a motion capture system and two force plates respectively. RESULTS: Paired-samples t-test results showed participants 1RM under HBD conditions (142.5 ± 47.2 kg) was greater than under BS conditions (108.0 ± 37.3 kg; t(15) = −7.30p\u3c 0.05). Data also showed that participants adopted greater trunk lean under max load in the bottom position of the HBD (69.5±6.9°) compared to that of the BS (48.6± 7.3°; θ trunk; t(15)= 9.76; p\u3c .01). Participants also exhibited a more extended knee position in the bottom position of the HBD (93.1± 11.4°) relative to the BS (119.5± 8.4°; t(15)= 6.42; p\u3c .01). In addition, participants exhibited greater M hip under BS (-227.4± 69.4Nm) relative to HBD conditions (-136.7± 75.1 Nm; t(15)= -6.55; p\u3c .001). Examination of knee joint moments revealed no difference in M knee between exercises (t(15)= -1.67; p= .116). CONCLUSION: At maximum loads, these exercises are not the same based on the mechanical differences experienced. These results suggest that at maximal loads (100% 1-RM) that strength coaches may not want to use these exercises interchangeably

CAG repeat expansion in Huntington disease determines age at onset in a fully dominant fashion

Objective: Age at onset of diagnostic motor manifestations in Huntington disease (HD) is strongly correlated with an expanded CAG trinucleotide repeat. The length of the normal CAG repeat allele has been reported also to influence age at onset, in interaction with the expanded allele. Due to profound implications for disease mechanism and modification, we tested whether the normal allele, interaction between the expanded and normal alleles, or presence of a second expanded allele affects age at onset of HD motor signs. Methods: We modeled natural log-transformed age at onset as a function of CAG repeat lengths of expanded and normal alleles and their interaction by linear regression. Results: An apparently significant effect of interaction on age at motor onset among 4,068 subjects was dependent on a single outlier data point. A rigorous statistical analysis with a wellbehaved dataset that conformed to the fundamental assumptions of linear regression (e.g., constant variance and normally distributed error) revealed significance only for the expanded CAG repeat, with no effect of the normal CAG repeat. Ten subjects with 2 expanded alleles showed an age at motor onset consistent with the length of the larger expanded allele. Conclusions: Normal allele CAG length, interaction between expanded and normal alleles, and presence of a second expanded allele do not influence age at onset of motor manifestations, indicating that the rate of HD pathogenesis leading to motor diagnosis is determined by a completely dominant action of the longest expanded allele and as yet unidentified genetic or environmental factors. Copyright © 2012 by AAN Enterprises, Inc