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.

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.

Is the control of movement less stable when we walk or run in challenging settings? Intuitively, one might answer that it is, given that challenging locomotion externally (e.g., rough terrain) or internally (e.g., age-related impairments) makes our movements more unstable. Here, we investigated how young and old humans synergistically activate muscles during locomotion when different perturbation levels are introduced. Of these control signals, called muscle synergies, we analyzed the local stability and the complexity (or irregularity) over time. Surprisingly, we found that perturbations force the central nervous system to produce muscle activation patterns that are less unstable and less complex. These outcomes show that robust locomotion control in challenging settings is achieved by producing less complex control signals that are more stable over time, whereas easier tasks allow for more unstable and irregular control.

Possibilities and limitations in the biomechanical analysis of countermovement jump performance were examined using force plate data. Four male and 4 female sport students participated in the study. Software designed to test jumping performance was used to evaluate recordings from a force plate and to compute net velocity and net displacement measures for the center of gravity. In parallel, a film analysis incorporating Dempster's center of gravity model was used for a comparison. Validity of the computed kinetic measures was evaluated with a general analysis of the major error sources including the data acquisition and numerical computations. Numerical integration procedures were found to be a reasonable tool for calculating net velocity and net displacement parameters for a more detailed analysis of athletic jumping performance. On the other hand, it appeared that Dempster-like center of gravity models can cause errors that disqualify their use as validation criteria for kinetic parameters.

BackgroundThe effectiveness of strength training on unstable surfaces (STU) versus stable surfaces (STS) or a control condition (CON; i.e. no training or regular training only) for strength, power and balance performance across the lifespan has not yet been investigated in a systematic review and meta-analysis.ObjectiveThe aims of this systematic review and meta-analysis were to determine the general effects of STU versus STS or CON on muscle strength, power and balance in healthy individuals across the lifespan and to investigate whether performance changes following STU are age specific.Data SourcesA computerized systematic literature search was performed in the electronic databases PubMed and Web of Science from January 1984 up to February 2015.Study Eligibility CriteriaInitially, 209 articles were identified for review. Only controlled trials were included if they investigated STU in healthy individuals and tested at least one measure of maximal strength, strength endurance, muscle power, or static/dynamic balance. In total, 22 studies met the inclusion criteria.Study Appraisal and Synthesis MethodsThe included studies were coded for the following criteria: age, sex, training status, training modality, exercise and test modality. Effect size measures included within-subject standardized mean differences (SMDw) and weighted between-subject standardized mean differences (SMDb). Heterogeneity between studies was assessed using I2 and χ2 statistics. The methodological quality of each study was assessed using the Physiotherapy Evidence Database (PEDro) Scale.ResultsOur search failed to identify studies that examined the effects of STU versus STS or CON in children and middle-aged adults. However, four studies were identified that investigated the effects of STU versus CON or STS in adolescents, 15 studies were identified in young adults and three studies were identified in old adults. Compared with CON, STU produced medium effects on maximal strength in young adults and no effects to medium effects in old adults. In addition, large effects were detected on strength endurance in adolescents and in young adults; in old adults, a small effect was found. With regard to muscle power, medium effects were observed in young adults and small effects were observed in old adults. Further, large effects were found for static and dynamic balance in old adults, but only a small effect was found for dynamic balance in young adults. The comparison of STU and STS revealed inconsistent results as indicated by training-induced changes in favour of STU, as well as STS. Small to medium effects were found for maximal strength in adolescents in favour of STS, and small effects were found in young adults in favour of STU. With regard to strength endurance, large effects were found in adolescents in favour of STS and small effects were found in favour of STU. Additionally, we detected small effects in young adults in favour of STU. In terms of muscle power, no effects were observed in adolescents but medium effects were found in favour of...

Acute bouts of static stretching have been shown to impair performance. Most published studies have incorporated static stretching that stressed the muscle(s) to the point of discomfort (POD). There are very few studies that have examined the effects of submaximal intensity (less than POD) static stretching on subsequent performance. Ten participants were pre-tested by performing two repetitions of three different stretches to assess range of motion (ROM) and two repetitions each of five different types of jumps. Following pre-testing, participants were stretched four times for 30 s each with 30 s recovery for the quadriceps, hamstrings and plantar flexors at 100% (POD), 75% and 50% of POD or a control condition. Five minutes following the stretch or control conditions, they were tested post-stretch with the same stretches and jumps as the pre-test. All three stretching intensities adversely affected jump heights. With data collapsed over stretching intensities, there were significant decreases in jump height of 4.6% (P=0.01), 5.7% (P<0.0001), 5.4% (P=0.002), 3.8% (P=0.009) and 3.6% (P=0.008) for the drop jump, squat jump, countermovement jump (CMJ) to a knee flexion of 70 degrees , CMJ using a preferred jump strategy and short amplitude CMJ respectively. An acute bout of maximal or submaximal intensity stretching can impair a variety of jumping styles and based on previous research, it is hypothesized that changes in muscle compliance may play a role.

The present findings indicate that modified feedforward mechanisms in terms of lower leg muscle activities during the preactivation phase and/or possible alterations in leg muscle activity shortly after ground contact (i.e., braking phase) are responsible for performance decrements during jumping on unstable surfaces.

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.