Comparison of vertical ground reaction forces during overground and treadmill running. A validation study.

BACKGROUND: One major drawback in measuring ground-reaction forces during running is that it is time consuming to get representative ground-reaction force (GRF) values with a traditional force platform. An instrumented force measuring treadmill can overcome the shortcomings inherent to overground testing. The purpose of the current study was to determine the validity of an instrumented force measuring treadmill for measuring vertical ground-reaction force parameters during running. METHODS: Vertical ground-reaction forces of experienced runners (12 male, 12 female) were obtained during overground and treadmill running at slow, preferred and fast self-selected running speeds. For each runner, 7 mean vertical ground-reaction force parameters of the right leg were calculated based on five successful overground steps and 30 seconds of treadmill running data. Intraclass correlations (ICC3,1) and ratio limits of agreement (RLOA) were used for further analysis. RESULTS: Qualitatively, the overground and treadmill ground-reaction force curves for heelstrike runners and non-heelstrike runners were very similar. Quantitatively, the time-related parameters and active peak showed excellent agreement (ICCs between 0.76 and 0.95, RLOA between 5.7% and 15.5%). Impact peak showed modest agreement (ICCs between 0.71 and 0.76, RLOA between 19.9% and 28.8%). The maximal and average loading-rate showed modest to excellent ICCs (between 0.70 and 0.89), but RLOA were higher (between 34.3% and 45.4%). CONCLUSIONS: The results of this study demonstrated that the treadmill is a moderate to highly valid tool for the assessment of vertical ground-reaction forces during running for runners who showed a consistent landing strategy during overground and treadmill running. The high stride-to-stride variance during both overground and treadmill running demonstrates the importance of measuring sufficient steps for representative ground-reaction force values. Therefore, an instrumented treadmill seems to be suitable for measuring representative vertical ground-reaction forces during running.

The effectiveness of a preconditioning programme on preventing running-related injuries in novice runners: a randomised controlled trial.

OBJECTIVES: There is no consensus on the aetiology and prevention of running-related injuries in runners. Preconditioning studies among different athlete populations show positive effects on the incidence of sports injuries. HYPOTHESIS: A 4-week preconditioning programme in novice runners will reduce the incidence of running-related injuries. STUDY DESIGN: Randomised controlled clinical trial; level of evidence, 1. METHODS: Novice runners (N=432) prepared for a four-mile recreational running event. Participants were allocated to the 4-week preconditioning (PRECON) group (N=211) or the control group (N=221). The PRECON group started a 4-week training programme, prior to the running programme, with walking and hopping exercises. After the 4-week period both groups started a 9-week running programme. In both groups information was registered on running exposure and running-related injuries (RRIs) using an internet-based running log. Primary outcome measure was RRIs per 100 runners. An RRI was defined as any musculoskeletal complaint of the lower extremity or lower back causing restriction of running for at least a week. RESULTS: The incidence of RRIs was 15.2% in the PRECON group and 16.8% in the control group. The difference in RRIs between the groups was not significant (χ(2)=0.161, df=1, p=0.69). CONCLUSION: This prospective study demonstrated that a 4-week PRECON programme with walking and hopping exercises had no influence on the incidence of RRIs in novice runners.

The GRONORUN 2 study: effectiveness of a preconditioning program on preventing running related injuries in novice runners. The design of a randomized controlled trial.

BACKGROUND: Distance running is a popular recreational exercise. It is a beneficial activity for health and well being. However, running may also cause injuries, especially of the lower extremities. In literature there is no agreement what intrinsic and extrinsic factors cause running related injuries (RRIs). In theory, most RRIs are elicited by training errors, this too much, too soon. In a preconditioning program runners can adapt more gradually to the high mechanical loads of running and will be less susceptible to RRIs. In this study the effectiveness of a 4-week preconditioning program on the incidence of RRIs in novice runners prior to a training program will be studied. METHODS/DESIGN: The GRONORUN 2 (Groningen Novice Running) study is a two arm randomized controlled trial studying the effect of a 4-week preconditioning (PRECON) program in a group of novice runners. All participants wanted to train for the recreational Groningen 4-Mile running event. The PRECON group started a 4-week preconditioning program with walking and hopping exercises 4 weeks before the start of the training program. The control (CON) and PRECON group started a frequently used 9-week training program in preparation for the Groningen 4-Mile running event.During the follow up period participants registered their running exposure, other sporting activities and running related injuries in an Internet based running log. The primary outcome measure was the number of RRIs. RRI was defined as a musculoskeletal ailment or complaint of the lower extremities or back causing a restriction on running for at least three training sessions. DISCUSSION: The GRONORUN 2 study will add important information to the existing running science. The concept of preconditioning is easy to implement in existing training programs and will hopefully prevent RRIs especially in novice runners. TRIAL REGISTRATION: The Netherlands National Trial Register NTR1906. The NTR is part of the WHO Primary Registries.

Observation, imagination and execution of an effortful movement: more evidence for a central explanation of motor imagery.

In this study subjects had to imagine, observe and perform a series of 25 squat movements while lifting two dumbbells of 12.5 kg each (one with each hand). This movement is effortful and requires substantial activation of peripheral systems. It was asked whether subjects when they imagined that they were performing the movements or when they observed a model performing the squat movements would show increased activity in EMG, heart rate and respiration compared with a control condition where they sat relaxed in a comfortable chair or a condition where they actually performed the squat movements. Two groups of subjects participated in the experiment: experienced squatters and novices. By employing these two groups we were able to study the differential effect of earlier experience with the target movement on peripheral activation. The results showed that with the exception of respiration no significant peripheral activation could be measured related to motor imagery. Although a clear distinction in experience existed between the experienced squatters versus the novices, no relevant imagery-related differences could be obtained between the two groups. The results are discussed in the light of a central explanation of motor imagery.

The role of motor imagery in learning a totally novel movement.

The aim of the present study is to gain more insight into the mechanisms underlying mental practice. The question of whether a totally novel movement may be learned by mental practice was investigated. Healthy young adults had to learn the abduction of the big toe (dominant right foot) without moving the other toes or the foot. The subjects were divided into two groups: subjects who were absolutely unable to abduct their big toe ("absolute zero" group) and subjects who were able to abduct their toe to some extent but showed clear room for improvement ("already doing it" group). Two separate experiments were executed. In the first experiment, 37 absolute-zero subjects had to practice, mentally or physically, the target movement. In the second experiment 40 already-doing-it subjects had to improve their toe-abduction skill. The results showed that absolute-zero subjects could not acquire the toe-abduction movement by means of mental practice. Only subjects who physically practiced the target movement improved significantly. Subjects who had some experience in the task (already-doing-it subjects) improved significantly after mental practice as well as after physical practice. The results seem to indicate that it is more plausible to explain the learning effects of mental practice in terms of a "top-down" mechanism based on the activation of a central representation of the movement than in terms of a peripheral "bottom-up" mechanism based on the activation of muscles.