Sandro Nigg

Unstable shoes: functional concepts and scientific evidence

The purpose of this study was to discuss (a) the conceptual idea behind unstable footwear and (b) the validity and scientific support of some selected claims made with respect to unstable shoes. The concept is that unstable shoes are built to provide a training device that uses instability as a strategy to train and strengthen muscles in the human locomotor system. Specific claims are: (1) evidence shows that unstable shoes currently on the market produce a substantial and significant increase in instability. The effects are most evident during standing but are also apparent in walking. (2) Unstable shoes increase the activity in certain muscles in about 80% of the population. The affected muscles change between different subjects. The highest relative increases were found in the small muscles crossing the ankle joint complex. (3) ‘Muscle toning’ is not defined and experimental data associating ‘muscle toning’ with unstable shoes are not available. (4) There is evidence that unstable shoes improve the static balance performance of users whose balance skills are low. (5) There is indirect evidence that unstable shoes reduce forces in the joints of the lower extremities. (6) There is evidence that unstable shoes can reduce the level of perceived pain. This has been confirmed in subjects suffering from pain in the knee joint and for subjects with low back pain. Based on these results, it seems that unstable shoes are associated with several possible benefits. However, the effects are not consistent between different subjects. In our experience, positive effects can be shown for about 80% of the test subjects.

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.

The effects of a temporarily manipulated dental occlusion on the position of the spine: a comparison during standing and walking

BACKGROUND CONTEXT The relationship between dental occlusion and body posture or even the spine position is often analyzed and confirmed. However, this relationship has not been systematically investigated for standing and walking. PURPOSE To examine whether a symmetric or asymmetric dental occlusion block, using 4 mm thick silicon panels, can significantly change the spine position (cervical, thoracic, or lumbar region) during standing and walking. STUDY DESIGN The following study is a cross-sectional study. PATIENT SAMPLE This study was carried out with 23 healthy subjects (18 women, 5 men) without discomfort in the temporomandibular system or body movement apparatus. OUTCOME MEASURES Position changes (millimeter) of the spine (cervical, thoracic, lumbar) in frontal, sagittal, and transverse planes of motion. METHODS The upper spine position was quantified with an ultrasonic distance measurement system (sonoSens Monitor). Every subject placed the 4 mm thick silicon panel systematically between the left/right premolars or the front teeth. Differences between the habitual and manipulated occlusion positions were determined by the Friedman test, followed by pairwise comparisons with applied Bonferroni-Holm correction. RESULTS During standing and walking there were significant (p≤.05) differences between the occlusion block conditions and the habitual dental position in all body planes except in the right lumbar region during walking. In addition, differences within the manipulated occlusion position could be detected. Significant differences were also shown between the standing and walking trials in the frontal, sagittal, and transverse planes, particularly with respect to the lumbar region (p≤.001). CONCLUSIONS Symmetrical and asymmetrical occlusion blocks in the premolar region can be associated with changes in all three spine regions during standing and walking. The results showed highly similar reaction patterns in all spine positions, regardless of the location of the silicon panel. Between standing and walking, the main differences were in the lumbar spine. The results suggest a relationship between the chewing and the movement system. However, it must be stated that this study has no direct clinical impact. The study design cannot determine the causality of the observed associations; also the clinical significance of the small postural changes remains unknown.

An On-Ice Measurement Approach to Analyse the Biomechanics of Ice Hockey Skating

Skating is a fundamental movement in ice hockey; however little research has been conducted within the field of hockey skating biomechanics due to the difficulties of on-ice data collection. In this study a novel on-ice measurement approach was tested for reliability, and subsequently implemented to investigate the forward skating technique, as well as technique differences across skill levels. Nine high caliber (High) and nine low caliber (Low) hockey players performed 30m forward skating trials. A 3D accelerometer was mounted to the right skate for the purpose of stride detection, with the 2nd and 6th strides defined as acceleration and steady-state, respectively. The activity of five lower extremity muscles was recorded using surface electromyography. Biaxial electro-goniometers were used to quantify hip and knee angles, and in-skate plantar force was measured using instrumented insoles. Reliability was assessed with the coefficient of multiple correlation, which demonstrated moderate (r>0.65) to excellent (r>0.95) scores across selected measured variables. Greater plantar-flexor muscle activity and hip extension were evident during acceleration strides, while steady state strides exhibited greater knee extensor activity and hip abduction range of motion (p<0.05). High caliber exhibited greater hip range of motion and forefoot force application (p<0.05). The successful implementation of this on-ice mobile measurement approach offers potential for athlete monitoring, biofeedback and training advice.

Measuring lateral shuffle and side cut performance

Abstract Whitting, JW, de Melker Worms, JLA, Maurer, C, Nigg, SR, and Nigg, BM. Measuring lateral shuffle and side cut performance. J Strength Cond Res 27(11): 3197–3203, 2013—Lateral shuffle and side cut (SSC) movements are defensive basketball movements where movement speed is critical to performance. The purpose of this study was to compare SSC data obtained using timing lights with motion capture system data and to determine the most appropriate method for measuring SSC performance. Shuffle time data were recorded using both timing lights and a motion capture system while 9 male subjects performed 2 different SSC movement sets, with and without controlling for arm movements, which may influence performance times. Shuffle and side cut times and SSC displacements were used to calculate mean shuffle velocity for each trial. The SEs for the motion capture system were estimated for SSC times (±4.2 milliseconds; ∼0.24% of mean shuffle time) and velocities (±5.5 mm·s−1; ∼0.24% of mean shuffle velocity), respectively, indicating high levels of precision. Timing light movement time variability was significantly higher during the uncontrolled (SD = 42 milliseconds) when compared with the controlled (SD = 9 milliseconds, p < 0.001) condition, indicating a significant reduction in variability by controlling non–performance-related variability such as arm movement. A significant positive correlation was found between SSC time and SSC displacement (r2 = 0.42) indicating that performance times were dependent on displacement. Furthermore, the variance in motion-captured SSC velocity was significantly smaller than the variance in velocity determined using timing lights (p < 0.05). We concluded that motion-captured SSC velocity data reduced systematic errors and non–performance-related movement variability and, therefore, was better able to reflect true performance. As true performance variability in human movement provides important information, the presented method for calculating SSC velocity in this study is recommended for assessing SSC performance.

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.

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.

Ankle muscle strength influence on muscle activation during dynamic and static ankle training modalities

Abstract Muscle weakness is considered a risk factor for ankle injury. Balance training and barefoot running have been used in an attempt to strengthen the muscles crossing the ankle. It is expected that training tasks that successfully strengthen the ankle would elicit increased muscular activity. However, it is unknown how an individuals ankle strength will influence the muscle activity used during a given task. Twenty-six participants performed dynamic (shod, barefoot running) and static tasks (squat on ground, squat on ®Bosu Ball) believed to strengthen the muscles surrounding the ankle. Electromyographic signals of the tibialis anterior, peroneus longus, gastrocnemius lateralis (GL) and gastrocnemius medialis (GM) were recorded and analysed using a non-linearly scaled wavelet analysis. Participants were divided into a strong group and a weak group according to their isometric plantar-flexion torque. The weak group required more relative GL and GM muscle activity during each training task compared to the strong group. No difference was observed between shod and barefoot running. There was a significant effect of training task on muscle activation level for the weak group. Differences in ankle strength had a significant impact on muscle activation.

A Novel Approach to Determine Strides, Ice Contact, and Swing Phases During Ice Hockey Skating Using a Single Accelerometer.

This study presents a new approach for automated identification of ice hockey skating strides and a method to detect ice contact and swing phases of individual strides by quantifying vibrations in 3D acceleration data during the blade-ice interaction. The strides of a 30-m forward sprinting task, performed by 6 ice hockey players, were evaluated using a 3D accelerometer fixed to a hockey skate. Synchronized plantar pressure data were recorded as reference data. To determine the accuracy of the new method on a range of forward stride patterns for temporal skating events, estimated contact times and stride times for a sequence of 5 consecutive strides was validated. Bland-Altman limits of agreement (95%) between accelerometer and plantar pressure derived data were less than 0.019 s. Mean differences between the 2 capture methods were shown to be less than 1 ms for contact and stride time. These results demonstrate the validity of the novel approach to determine strides, ice contact, and swing phases during ice hockey skating. This technology is accurate, simple, effective, and allows for in-field ice hockey testing.