Jordyn Vienneau

Development of a symmetry index using discrete variables

The objective of this study was to introduce and evaluate a new methodology to quantify lower extremity movement symmetry using data from the stance phase in over-ground running. Seventeen subjects completed five heel-toe over-ground running trials per leg over a force platform at 3.33±0.5ms(-1) with retro-reflective markers on both legs and the pelvis. Thirty kinetic and kinematic variables were collected and 12 were chosen as important variables for calculating symmetry based on low variance of the data and their functional relevance with respect to symmetry. The developed formula uses the integral of the absolute value of the difference between the left and right leg during the stance phase. The results were divided into a sagittal, transverse, and frontal index, as well as a global index for all three planes of motion. This enabled analyses from both general and categorical perspectives, whereby individuals could be identified as symmetrical in one plane and asymmetrical in the other. The new methodology allows for the evaluation of symmetry over the entire stance phase and accounts for time lags between left and right legs. To learn more about symmetry during particular movements, future research should include larger cohorts, use consecutive force platforms, examine the flight phase of running and include subjects that are known to have asymmetrical gait.

Relationship Between Lower Limb Muscle Activity and Platform Acceleration During Whole-Body Vibration Exercise

Abstract Lienhard, K, Vienneau, J, Nigg, S, Meste, O, Colson, SS, and Nigg, BM. Relationship between lower limb muscle activity and platform acceleration during whole-body vibration exercise. J Strength Cond Res 29(10): 2844–2853, 2015—The purpose of this study was to identify the influence of different magnitudes and directions of the vibration platform acceleration on surface electromyography (sEMG) during whole-body vibration (WBV) exercises. Therefore, a WBV platform was used that delivers vertical vibrations by a side-alternating mode, horizontal vibrations by a circular mode, and vibrations in all 3 planes by a dual mode. Surface electromyography signals of selected lower limb muscles were measured in 30 individuals while they performed a static squat on a vibration platform. The WBV trials included 2 side-alternating trials (Side-L: 6 Hz, 2.5 mm; Side-H: 16 Hz, 4 mm), 2 circular trials (Circ-L: 14 Hz, 0.8 mm; Circ-H: 43 Hz, 0.8 mm), and 4 dual-mode trials that were the combinations of the single-mode trials (Side-L/Circ-L, Side-L/Circ-H, Side-H/Circ-L, Side-H/Circ-H). Furthermore, control trials without vibration were assessed, and 3-dimensional platform acceleration was quantified during the vibration. Significant increases in the root mean square of the sEMG (sEMGRMS) compared with the control trial were found in most muscles for Side-L/Circ-H (+17 to +63%, p ⩽ 0.05), Side-H/Circ-L (+7 to +227%, p ⩽ 0.05), and Side-H/Circ-H (+21 to +207%, p < 0.01) and in the lower leg muscles for Side-H (+35 to +138%, p ⩽ 0.05). Furthermore, only the vertical platform acceleration showed a linear relationship (r = 0.970, p < 0.001) with the averaged sEMGRMS of the lower limb muscles. Significant increases in sEMGRMS were found with a vertical acceleration threshold of 18 m·s−2 and higher. The present results emphasize that WBV exercises should be performed on a platform that induces vertical accelerations of 18 m·s−2 and higher.

Soccer shoe bending stiffness significantly alters game-specific physiology in a 25-minute continuous field-based protocol

The purpose of this study was to investigate the effects of soccer shoes with differing bending stiffness on physiological and performance variables in a game-like situation. A sample of 13 male soccer players was recruited to complete this study. Three soccer shoes with different forefoot bending stiffness (low, medium, high) were compared using a continuous field-based work protocol (the Soccer-25). Participants performed the Soccer-25 while the physiological (rate of oxygen consumption, heart rate, ventilation, and rate of energy expenditure) and performance variables (drill completion times) were recorded. The Soccer-25 consists of seven phases, Drills 1–3 and Shuttle Runs 1–4. A one-way repeated measures ANOVA was used to determine whether there were any significant effects for soccer shoe condition for each of the physiological and performance variables. The medium-stiffness shoe was significantly lower than the high-stiffness shoe for a number of physiological variables, including global oxygen consumption (p = 0.044), heart rate during Drills 2 (p = 0.043), ventilation during Shuttle Run 4 (p = 0.016), global energy expenditure (p = 0.043), and rate of energy expenditure during Drills 1 (p = 0.044). The low stiffness shoe was not significantly different from the medium- or high-stiffness shoes. No significant differences were found for any of the performance variables. Soccer shoe forefoot bending stiffness significantly affects the physiological variables in a game-like situation.

Assessing Footwear Effects from Principal Features of Plantar Loading during Running

PURPOSE The effects of footwear on the musculoskeletal system are commonly assessed by interpreting the resultant force at the foot during the stance phase of running. However, this approach overlooks loading patterns across the entire foot. An alternative technique for assessing foot loading across different footwear conditions is possible using comprehensive analysis tools that extract different foot loading features, thus enhancing the functional interpretation of the differences across different interventions. The purpose of this article was to use pattern recognition techniques to develop and use a novel comprehensive method for assessing the effects of different footwear interventions on plantar loading. METHODS A principal component analysis was used to extract different loading features from the stance phase of running, and a support vector machine (SVM) was used to determine whether and how these loading features were different across three shoe conditions. RESULTS The results revealed distinct loading features at the foot during the stance phase of running. The loading features determined from the principal component analysis allowed successful classification of all three shoe conditions using the SVM. Several differences were found in the location and timing of the loading across each pairwise shoe comparison using the output from the SVM. CONCLUSIONS The analysis approach proposed can successfully be used to compare different loading patterns with a much greater resolution than has been reported previously. This study has several important applications. One such application is that it would not be relevant for a user to select a shoe or for a manufacturer to alter a shoes construction if the classification across shoe conditions would not have been significant.

The Effect of Whole-body Vibration on Muscle Activity in Active and Inactive Subjects.

The purpose of this study was to compare lower limb muscle activity between physically active and inactive individuals during whole-body vibration exercises. Additionally, transmissibility of the vertical acceleration to the head was quantified. 30 active and 28 inactive participants volunteered to stand in a relaxed (20°) and a squat (60°) position on a side-alternating WBV platform that induced vibrations at 16 Hz and 4 mm amplitude. Surface electromyography (sEMG) was measured in selected lower limb muscles and was normalized to the corresponding sEMG recorded during a maximal voluntary contraction. The vertical acceleration on the head was evaluated and divided by the vertical platform acceleration to obtain transmissibility values. Control trials without vibration were also assessed. The outcomes of this study showed that (1) WBV significantly increased muscle activity in the active (absolute increase: +7%, P <0.05) and inactive participants (+8%, P <0.05), (2) with no differences in sEMG increases between the groups (P>0.05). However, (3), transmissibility to the head was greater in the active (0.080) than the inactive participants (0.065, P <0.05). In conclusion, inactive individuals show similar responses in sEMG due to WBV as their active counterparts, but are at lower risk for potential side-effects of vibration exposure.

The Preferred Movement Path Paradigm: Influence of Running Shoes on Joint Movement

Purpose (A) To quantify differences in lower extremity joint kinematics for groups of runners subjected to different running footwear conditions, and (B) to quantify differences in lower extremity joint kinematics on an individual basis for runners subjected to different running footwear conditions. Methods Three-dimensional ankle and knee joint kinematics were collected for 35 heel–toe runners when wearing three different running shoes and when running barefoot. Absolute mean differences in ankle and knee joint kinematics were computed between running shoe conditions. The percentage of individual runners who displayed differences below a 2°, 3°, and 5° threshold were also calculated. Results The results indicate that the mean kinematics of the ankle and knee joints were similar between running shoe conditions. Aside from ankle dorsiflexion and knee flexion, the percentage of runners maintaining their movement path between running shoes (i.e., less than 3°) was in the order of magnitude of about 80% to 100%. Many runners showed ankle and knee joint kinematics that differed between a conventional running shoe and barefoot by more than 3°, especially for ankle dorsiflexion and knee flexion. Conclusions Many runners stay in the same movement path (the preferred movement path) when running in various different footwear conditions. The percentage of runners maintaining their preferred movement path depends on the magnitude of the change introduced by the footwear condition.

Older adults show higher increases in lower-limb muscle activity during whole-body vibration exercise

The purpose of this study was to compare lower limb muscle activity during whole-body vibration (WBV) exercise between a young and an older study population. Thirty young (25.9±4.3yrs) and thirty older (64.2±5.3yrs) individuals stood on a side-alternating WBV platform while surface electromyography (sEMG) was measured for the tibialis anterior (TA), gastrocnemius medialis (GM), soleus (SOL), vastus lateralis (VL), vastus medialis (VM), and biceps femoris (BF). The WBV protocol included nine vibration settings consisting of three frequencies (6, 11, 16Hz) x three amplitudes (0.9, 2.5, 4.0mm), and three control trials without vibration (narrow, medium, wide stance). The vertical platform acceleration (peak values of maximal displacement from equilibrium) was quantified during each vibration exercise using an accelerometer. The outcomes of this study showed that WBV significantly increased muscle activity in both groups for most vibration conditions in the TA (averaged absolute increase: young: +3.9%, older: +18.4%), GM (young: +4.1%, older: +9.5%), VL (young: +6.3%, older: +12.6%) and VM (young: +5.4%, older: +8.0%), and for the high frequency-amplitude combinations in the SOL (young: +7.5%, older: +12.6%) and BF (young: +1.9%, older: +7.5%). The increases in sEMG activity were significantly higher in the older than the young adults for all muscles, i.e., TA (absolute difference: 13.8%, P<0.001), GM (4.6%, P=0.034), VL (7.6%, P=0.001), VM (6.7%, P=0.042), BF (6.4%, P<0.001), except for the SOL (0.3%, P=0.248). Finally, the vertical platform acceleration was a significant predictor of the averaged lower limb muscle activity in the young (r=0.917, P<0.001) and older adults (r=0.931, P<0.001). In conclusion, the older population showed greater increases in lower limb muscle activity during WBV exercise than their young counterparts, meaning that they might benefit more from WBV exercises. Additionally, training intensity can be increased by increasing the vertical acceleration load.

Assessment of lower body toning with quantitative variables

Purpose: Development of a multifactorial equation to define lower body muscle toning with quantitative variables. Methods: Eight subjects with different levels of toning were used as an input. A set of 11 parameters covering soft tissue characteristics and body composition were correlated with a subjective rating of toning using a visual analogue scale (VAS). The variables with the highest correlation were combined using a principal component method. A subspace spanned by principal components explaining 95% of the variability was used for the further analysis. This subspace was rotated until the first axis had the highest correlation with the subjective toning rating. An equation based on this first axis was used to calculate a quantitative toning rating. Results: Five discrete variables including both body composition (body fat, ectomorphy and endomorphy) and soft tissue characteristics (trunk forward flexion and normalized peak torque of knee flexion) lead to a high correlation with the expert rating of toning. The coefficient of determination was r 2 = 0.977 ± 0.008. Conclusion: The method developed in this paper allows for a quantitative calculation of lower body toning. The presented method allows for easy integration of more subjects, which would lead to a stable definition of the level of lower body toning based on the combination of quantitative measurable variables.