Armin Kibele

SEVEN WEEKS OF INSTABILITY AND TRADITIONAL RESISTANCE TRAINING EFFECTS ON STRENGTH, BALANCE AND FUNCTIONAL PERFORMANCE

The objective of the study was to compare the effect of a 7-week unstable and stable resistance training program on measures of strength, balance, and functional performance. Forty participants were divided into unstable or stable resistance training groups. Training was conducted twice a week for 7 weeks. Pre- and post-testing measures included leg extension strength, static and dynamic balance, sit-ups, long jump, hopping test for time, shuttle run, and sprint. Results showed that there was no overall difference between unstable and stable resistance training and the training effects were independent of gender. All measures except sprint time improved with training. Interaction effects demonstrated that unstable resistance training did provide an advantage for number of sit-ups performed (p = 0.03; 8.9%) and the right leg hopping test (6.2%; p = 0.0001). This study has demonstrated that instability resistance training may be considered as effective as traditional stable resistance training for inexperienced resistance trainers. Based on the present study and the literature, instability resistance training should be incorporated in conjunction with traditional stable training to provide a greater variety of training experiences without sacrificing training benefits.

Neuromodulation of aerobic exercise - A review

Running, and aerobic exercise in general, is a physical activity that increasingly many people engage in but that also has become popular as a topic for scientific research. Here we review the available studies investigating whether and to which degree aerobic exercise modulates hormones, amino acids, and neurotransmitters levels. In general, it seems that factors such as genes, gender, training status, and hormonal status need to be taken into account to gain a better understanding of the neuromodular underpinnings of aerobic exercise. More research using longitudinal studies and considering individual differences is necessary to determine actual benefits. We suggest that, in order to succeed, aerobic exercise programs should include optimal periodization, prevent overtraining and be tailored to interindividual differences, including neuro-developmental and genetically-based factors.

Neuromuscular fatigue recovery following rapid and slow stretch–shortening cycle movements

The purpose of this study was to investigate underlying mechanisms and neuromuscular recovery patterns following rapid and slow stretch-shortening cycle (SSC) movements performed to fatigue. Fourteen (10 moderately trained (MT) and four highly trained (HT)) subjects completed rapid and slow SSC movements to fatigue. The rapid SSC movement consisted of continuous drop jumps from a 30 cm platform until a predetermined jump height was no longer maintained, and the slow SSC movement consisted of continuous squats to 90° of knee flexion at a load of 65% of subjects one-repetition maximum until no further repetitions could be completed. Although blood lactate measures were significantly (p < 0.002) higher after the rapid SSC condition versus after the slow SSC condition, the recovery of neuromuscular properties (maximum voluntary contractions, twitch force, muscle compound action potential) following the two conditions to fatigue did not differ. The duration of the rapid SSC movement was dependent on the training status of the subject; HT subjects performed the rapid SSC longer (68.2%) than the MT subjects until fatigued. Thus, the neuromuscular fatigue recovery patterns were independent of the type of SSC movement, condition duration, and subject training status. Because rapid and slow SSC exercises induce similar fatigue patterns, training programs incorporating rapid SSC exercises can be developed similar to that prescribed in traditional slow SSC resistance training programs.

Down with Retirement: Implications of Embodied Cognition for Healthy Aging.

Cognitive and neurocognitive approaches to human healthy aging attribute age-related decline to the biologically caused loss of cognitive-control functions. However, an embodied-cognition approach to aging implies a more interactive view according to which cognitive control emerges from, and relies on a person’s active encounters with his or her physical and social environment. We argue that the availability of cognitive-control resources does not only rely on biological processes but also on the degree of active maintenance, that is, on the systematic use of the available control resources. Unfortunately, there is evidence that the degree of actual use might systematically underestimate resource availability, which implies that elderly individuals do not fully exploit their cognitive potential. We discuss evidence for this possibility from three aging-related issues: the reduction of dopaminergic supply, loneliness, and the loss of body strength. All three phenomena point to a downward spiral, in which losses of cognitive-control resources do not only directly impair performance but also more indirectly discourage individuals from making use of them, which in turn suggests underuse and a lack of maintenance—leading to further loss. On the positive side, the possibility of underuse points to not yet fully exploited reservoirs of cognitive control, which calls for more systematic theorizing and experimentation on how cognitive control can be enhanced, as well as for reconsiderations of societal practices that are likely to undermine the active maintenance of control resources—such as retirement laws.

Sex-Specific effects of surface instability on drop jump and landing biomechanics

This study investigated sex-specific effects of surface instability on kinetics and lower extremity kinematics during drop jumping and landing. Ground reaction forces as well as knee valgus and flexion angles were tested in 14 males (age: 23±2 years) and 14 females (age: 24±3 years) when jumping and landing on stable and unstable surfaces. Jump height was found to be significantly lower (9%, p<0.001) when drop jumps were performed on unstable vs. stable surface. Significantly higher peak ground reaction forces were observed when jumping was performed on unstable versus stable surfaces (5%, p=0.022). Regarding frontal plane kinematics during jumping and landing, knee valgus angles were higher on unstable compared to stable surfaces (19-32%, p<0.05). Additionally, at the onset of ground contact during landings, females showed higher knee valgus angles than males (222%, p=0.027). Sagittal plane kinematics indicated significantly smaller knee flexion angles (6-35%, p<0.05) when jumping and landing on unstable vs. stable surfaces. During drop jumps and landings, women showed smaller knee flexion angles at ground contact compared to men (27-33%, p<0.05). These findings imply that knee motion strategies were modified by surface instability and sex during drop jumps and landings.

Challenging human locomotion: stability and modular organisation in unsteady conditions

The need to move over uneven terrain is a daily challenge. In order to face unexpected perturbations due to changes in the morphology of the terrain, the central nervous system must flexibly modify its control strategies. We analysed the local dynamic stability and the modular organisation of muscle activation (muscle synergies) during walking and running on an even- and an uneven-surface treadmill. We hypothesized a reduced stability during uneven-surface locomotion and a reorganisation of the modular control. We found a decreased stability when switching from even- to uneven-surface locomotion (p < 0.001 in walking, p = 0.001 in running). Moreover, we observed a substantial modification of the time-dependent muscle activation patterns (motor primitives) despite a general conservation of the time-independent coefficients (motor modules). The motor primitives were considerably wider in the uneven-surface condition. Specifically, the widening was significant in both the early (+40.5%, p < 0.001) and late swing (+7.7%, p = 0.040) phase in walking and in the weight acceptance (+13.6%, p = 0.006) and propulsion (+6.0%, p = 0.041) phase in running. This widening highlighted an increased motor output’s robustness (i.e. ability to cope with errors) when dealing with the unexpected perturbations. Our results confirmed the hypothesis that humans adjust their motor control strategies’ timing to deal with unsteady locomotion.

The biomechanical structure of swim start performance

Abstract The aim of this study was to analyse the significance of various biomechanical parameters in swim start performance for the grab and track start techniques. To do so, structural equation models were analysed, incorporating measurements for the take-off phase, flight phase and entry phase. Forty-six elite German swimmers (18 female and 28 male; age: 20.1 ± 4.2 yrs; PB (100 m Freestyle): 53.6 ± 2.9 s) participated in the study. Their swim start performance was examined within a 25-m sprint test. Structural equation modelling was conducted in separate models for the block time, flight time and water time and in a combined model for swim start time. Our main finding was that swim start time is predominantly related to water time and determined to a lesser extent by block time and flight time. We conclude that more emphasis should be given to the water immersion behaviour and the gliding phase when analysing swim start performance. Furthermore, significant differences were found between the grab start and track techniques as regards the biomechanical parameters representing the take-off phase and water phase.

Automatic identification of gait events during walking on uneven surfaces

The accurate detection of gait events is essential for clinical gait analysis. Aside from speed, surface characteristics like planarity and compliance can affect gait kinematics. Therefore detection of kinematic gait events on uneven surfaces may be inaccurate. To date, no study has investigated the possible influence of surface characteristics on gait event detection. Thus, the purpose of this study was to assess and compare the performance of four kinematic-based gait event detection algorithms (horizontal heel-heel displacement, foot velocity, heel/toe-PSIS displacement, peak hip extension) during walking on three surfaces with different degrees of planarity. Kinematic and force plate data were collected on thirteen athletes during two self-selected walking speeds at a normal (1.30±0.03m/s) and fast pace (1.70±0.10m/s). Footstrike and toe-off events were calculated by the algorithms and compared to vertical ground reaction force as a reference. The main findings of the study were: (1) surface configuration had an effect on algorithm accuracy (p<0.010, 0.84<d<2.79); (2) the vertical foot-velocity profile provided the lowest RMSE for footstrike (8.8-14.6ms) during normal walking and toe-off (15.4-24.9ms) during normal and fast walking on all surfaces; (3) horizontal heel-ankle displacement provided the lowest RMSE for footstrike during fast walking on all surfaces (RMSE: 8.9-13.8ms). Overall, the vertical foot-velocity algorithm provided low RMSE for all conditions, is easy to apply and thus recommended for gait event detection.

Action induction by visual perception of rotational motion.

A basic process in the planning of everyday actions involves the integration of visually perceived movement characteristics. Such processes of information integration often occur automatically. The aim of the present study was to examine whether the visual perception of spatial characteristics of a rotational motion (rotation direction) can induce a spatially compatible action. Four reaction time experiments were conducted to analyze the effect of perceiving task irrelevant rotational motions of simple geometric figures as well as of gymnasts on a horizontal bar while responding to color changes in these objects. The results show that the participants react faster when the directional information of a rotational motion is compatible with the spatial characteristics of an intended action. The degree of complexity of the perceived event does not play a role in this effect. The spatial features of the used biological motion were salient enough to elicit a motion based Simon effect. However, in the cognitive processing of the visual stimulus, the critical criterion is not the direction of rotation, but rather the relative direction of motion (direction of motion above or below the center of rotation). Nevertheless, this conclusion is tainted with reservations since it is only fully supported by the response behavior of female participants.

Simon effects in action sequences

Most actions we perform in daily life consist of multiple movement elements. In two Simon task experiments, we investigated the impact of stimulus–response compatibility on planning and execution of action sequences. A total of 38 participants were instructed to perform action sequences consisting of multiple key presses (two to four key presses) as response to a left- or right-presented colored stimulus. Within one block, the requested action sequences were of the same length but differed in their spatial features. The results show Simon effects in reaction time for up to four-element long action sequences. The effects became especially apparent when participants were forced to finish action planning before action execution by the implementation of a no-go condition (Experiment 2). Simon effects in movement time emerged for two movement element actions, only. That is, dimensional overlap between spatial features embedded in an action sequence as well as in an imperative stimulus can affect action initiation.