Michael Buchecker

Improved postural control after slackline training is accompanied by reduced H-reflexes

“Slacklining” represents a modern sports activity where people have to keep balance on a tightened ribbon. The first trials on the slackline result in uncontrollable lateral swing of the supporting leg. Training decreases those oscillations and therefore improves postural control. However, the underlying neural mechanisms are not known. Therefore, the present study aimed to highlight spinal adaptations going along with slackline training. Twenty‐four subjects were either assigned to a training or a control group and postural control was assessed before and after the 10 training sessions. Additionally, soleus Hoffmann (H)‐reflexes were elicited to evaluate changes in the excitability of the spinal reflex circuitry. Trained subjects were able to maintain balance on the slackline for at least 20 s (P<0.001) and reduced platform movements on the balance board (P<0.05). The H‐reflexes were significantly diminished (P<0.05) while no changes occurred in the background electromyography (bEMG). The control group showed no significant changes. From a functional point of view the reflex reduction may serve to suppress uncontrollable reflex mediated joint oscillations. As the bEMG remained unchanged, presynaptic rather than post‐synaptic mechanisms are speculated to be responsible for the changes in the Ia‐afferent transmission.

Lower extremity joint loading during level walking with Masai barefoot technology shoes in overweight males

The purpose of this study was to evaluate the effects of Masai barefoot technology (MBT) shoes on lower extremity joint loading in overweight males during level walking. Therefore, lower extremity kinematics, kinetics, and muscle electromyographic signals of the vastus lateralis (VL), biceps femoris (BF), and gastrocnemius medialis (GM) were recorded in 10 overweight males at a self‐chosen walking speed with MBT shoes and conventional shoes. Selected peak joint moments, maximal joint force loading rates, mean muscle intensities, and co‐activation indices of the VL/BF, as well as of the VL/GM were analyzed and compared for the two shoe conditions using paired Students t‐tests (α=0.05). Results showed that walking with MBT shoes reduced first peak knee adduction moments in overweight subjects. During midstance and terminal stance, increases in VL/GM co‐activation, accompanied by increases in VL and GM (only terminal stance) intensities were found for the MBT situation. Kinetic variables analyzed to assess ankle and hip joint loading did not exhibit any statistical differences. These results suggest that using MBT shoes diminishes medial compartment loads at the knee without overloading hip or ankle joints in overweight males. However, the additional muscle loading should not be overlooked, and warrants further investigation.

Supervised slackline training improves postural stability

Abstract The present study investigated whether or not four weeks of supervised slackline training (SLT) performed on nylon webbing improves postural stability. Twenty-four healthy adults participated in the study and were assigned to either SLT (n=12) or a control (CON) group (n=12). The SLT group completed a four week training program, while the CON group received no training. Centre of gravity (COG) and joint angles (ankle, knee and hip) were calculated using whole body three-dimensional (3D) kinematic measurements during single leg standing on a stable surface (SS) and on a perturbed surface (PS) before and after training. After SLT, a significant interaction was found for the SS condition in anterior-posterior COG mean velocity, whereas no changes were observed in the medio-lateral direction or in joint kinematics. In the PS condition, the medio-lateral COG mean velocity, frontal angular range of motion in the knee and hip joint, sagittal angular mean velocity in the knee joint, as well as frontal angular mean velocity in the hip joint were reduced in the SLT group only (all P<0.05). No significant training effects were detected in the ankle joint kinematics in either group from pre to post test. Our findings demonstrate that four weeks of supervised SLT improves postural stability in single leg stance on a stable surface and/or during compensation of perturbations.

Effects of 4-week slackline training on lower limb joint motion and muscle activation

OBJECTIVES To investigate the effects of four weeks of slacklining on lower limb kinematics and muscle activity following a slip of the upright stance. DESIGN A randomized, gender matched study. METHODS Twenty-four young healthy adults participated in the study and were assigned to either a training or a control group. The training group completed a 4-week training program on slacklines, while the control group received no slackline training. Before and after training, participants performed single leg standing tasks on a moveable platform. During medio-lateral platform perturbation, platform displacement, lower limb joint motion (ankle, knee and hip) and surface electromyography (EMG) measurements from six lower limb muscles were recorded. RESULTS In the training group, a decrease in platform mean and maximum velocity (all p<0.05) was detected, but no changes were observed for the release time and maximum deflection (all p>0.05) of the platform. Regarding lower limb kinematics, a reduced corrective action was detected in the knee joint (p<0.05), whereas only a trend towards a decrease could be observed in the ankle joint (p<0.1). EMG data revealed an enhanced activation of the rectus femoris (p<0.05), as well as a trend to increased rectus femoris to biceps femoris co-activation (p=0.06) in the preparatory phase for training group. CONCLUSIONS The data strongly support that slacklining can improve postural control and enhance functional knee joint stability, which seems to be induced by enhanced preparatory muscle activation of the rectus femoris.

Spine kinematics and trunk muscle activity during bipedal standing using unstable footwear.

The current study was conducted to evaluate the effects of unstable footwear on spine kinematics and trunk muscle activity during bipedal stance. Therefore, spinal alignment and concurrent angular velocity measures were assessed in 27 asymptomatic adults while standing with unstable Masai Barefoot Technology (MBT) shoes and standard footwear, respectively, employing a multisegmental three‐dimensional trunk model. Electromyographic (EMG) analyses included recordings of the rectus abdominis, internal oblique, external oblique, upper thoracic paraspinals, lower thoracic erector spinae, and lumbar erector spinae. Kinematic and EMG variables were compared for the two shoe conditions via paired Students t‐tests (α = 0.05). Results showed that wearing unstable MBT shoes increased flexion at the mid‐thoracic level (0.8°; P = 0.001) and led to greater mean velocities of angular displacement at the thoracolumbar (11.2%; P = 0.003) and at the lumbopelvic (10.8%; P = 0.02) regions, accompanied by more lumbar erector spinae activity (18.2%; P = 0.003). Accordingly, using MBT shoes may have potential implications in promoting spine tissue health, notably at the low back area, through expected improvements in terms of muscle conditioning and/or motor performance. However, additional investigations are warranted to further examine the framework of unstable footwear constructions within prevention and rehabilitation settings.

The effect of different Masai Barefoot Technology (MBT) shoe models on postural balance, lower limb muscle activity and instability assessment

Unstable shoe constructions may counteract balance deficits and underutilization of lower limb muscles. The Masai Barefoot Technology (MBT) concept has been widely analysed in terms of footwear-induced instability. However, previous experiments investigated predominately one specific MBT shoe model. Therefore, the purpose of this experiment was to evaluate the effects of differently shaped MBT soles on stance biomechanics. Mean velocity of centre of pressure (CoP) displacement, root mean square (RMS) tibialis anterior (TA), peroneus longus (PL), gastrocnemius medialis (GM), vastus lateralis (VL) and biceps femoris (BF) activity, as well as subjective perception of instability were recorded in 31 young asymptomatic adults during standing with three different MBT models and a standard control shoe. Statistical analysis included repeated-measures ANOVAs with Bonferroni–Holm adjusted post-hoc tests. MBT footwear, regardless of shape and structure, significantly increased postural sway compared to the control condition. Additionally, there were significant differences between the MBT shoe types. These results coincided with those obtained from instability assessment testing. No significant effects of MBT footwear were detected for the GM and BF muscles. A consistent increase in TA, PL and VL RMS activity was only found for one MBT model. On a muscular level, within-MBT differences were statistically less pronounced than for CoP and for instability rating measures. These findings suggest that specific variations in MBT sole construction criteria differently challenged the postural control system without forfeiting the principal feature of simulating a less firm surface for the user. Further investigations are warranted to examine the framework of instability within the MBT concept, as well as associated intrinsic and extrinsic influences related to rehabilitation and prevention programmes.

Alpine Skiing With total knee ArthroPlasty (ASWAP): effects on strength and cardiorespiratory fitness.

This study investigated the effect of a 12‐week recreational skiing intervention on lower limb muscle strength and cardiorespiratory fitness in participants with unilateral total knee arthroplasty (TKA). Twenty‐seven older adults (70 ± 5 years) were assigned to the intervention (n = 13) or control group (n = 14) after surgery (2.5 ± 1 years). Leg muscle strength was measured using an IsoMed 2000 dynamometer and cardiorespiratory fitness was determined by cycle ergometry before and after the intervention as well as after an 8‐week retention period. The skiing intervention led to increased muscle strength in the operated leg during unilateral single joint isometric extension (maximal force: 11%; P < 0.05; rate of torque development: 24%; P < 0.05) and during the unilateral multi‐joint isokinetic single leg strength test (8%; P < 0.05). This resulted in a decreased asymmetry index in the isokinetic test (13% to 5%; P < 0.05). These adaptations remained unchanged toward the retention test. No effect was observed for cardiorespiratory fitness. The results demonstrate that muscle contraction forces required during recreational skiing in individuals with TKA seem adequate and effective to increase quadriceps and hamstrings muscle strength in the initially weaker operated leg and to reduce an augmented post‐operative asymmetry index.

Factors Discriminating High From Low Score Performance in Biathlon Shooting

PURPOSE To identify biomechanical predictors that distinguish between high- and low-score athletes in biathlon shooting and to determine the relationships among these variables in field testing. METHODS Twenty-two biathletes (8 female, 14 male) from the World Cup, the European Cup, and a federal youth squad each fired 3 clips of 5 shots in prone and standing shooting positions without physical load, followed by 2 respective series in both disciplines during a simulated 12.5-km pursuit race on roller skis. Biomechanical variables describing triggering, rifle force in the back shoulder, and body and rifle sway were calculated over the last 0.5 second before firing. For computed linear discriminant analyses, subjects were divided into high- and low-level performers based on mean scores for each condition separately. In addition, correlations among all biomechanical factors were calculated. RESULTS Regarding prone shooting, shoulder force in the rest condition and vertical rifle sway in the race simulation were shown to be main discriminators. Several body- and rifle-sway variables were found to be predictors in standing rest shooting. Body sway across the shooting line discriminated the groups in the standing race situation tendentially. Thus, the main performance predictors changed due to fatigue. Correlations between triggering and rifle sway, shoulder force and rifle sway, and body sway and rifle sway were discovered. CONCLUSIONS Referring to the current results, athletes are recommended to focus on vertical rifle sway in prone position and on body sway across the shooting line during standing shooting when fatigued.

Alpine Skiing With total knee ArthroPlasty (ASWAP): effects on gait asymmetries.

The aim of the study was to examine the effect of a 12‐week recreational skiing intervention on functional gait performance in people with unilateral total knee arthroplasty (TKA). Twenty‐three older adults (71 ± 5 years) were assigned to the intervention (IG) or control group (CG). Test time and ground reaction forces (GRF) were recorded at pre‐ and post‐intervention and in the retention phase during functional gait tests. Ground contact was recorded bilaterally and divided into the weight acceptance and push‐off phases. In IG, a faster stair descent time (16%) was observed at post‐test with no further change at the retention test. The asymmetry indices for all analyzed variables were decreased in stair descent and during weight acceptance in stair ascent and level walking without further changes between post‐ and retention test. The reduced asymmetries occurred mainly because of increased loading of the operated leg. Most variables were unchanged in CG. Similar to the force data, the asymmetry index for temporal stride characteristics was reduced in all stair descent variables. These results demonstrate that alpine skiing as a leisure‐time activity has a beneficial effect on gait performance and leads to a more balanced load distribution between the legs during daily activities.

Effect of Instability Training Equipment on Lower Limb Kinematics and Muscle Activity

To improve the effectiveness of training or therapy, it is important to know the benefits for each type of instability training equipment. The aim of this study was to show differences in lower limb kinematics and muscle activation during single leg standing on a slackline (SL) compared to a multi-functional rocker board (MD) and an air cushion (AC). In 14 subjects, mean angular velocity of the hip, knee and ankle, as well as the muscle activity (iEMG) from six lower limb muscles were recorded during 12 s of single leg standing task. Ankle in-/eversion and knee ab-/adduction angular velocity were highest for SL followed by MD and AC (all p < 0.05), as well as in the hip flex-/extension angular velocity with higher values for SL compared with AC (p < 0.01). Regarding iEMG, the rectus femoris muscle showed higher values for SL compared with MD (p < 0.05) and AC (p < 0.01). iEMG of biceps femoris muscle demonstrated higher values for MD compared to AC (p < 0.05), but with no difference to SL. Balancing on a SL is a more challenging exercise for the postural control system compared to MD and AC, and affects the knee and hip joint motion in particular.