Aim The purpose of this study was to determine the changes in running mechanics that occur when highly trained runners run barefoot and in a minimalist shoe, and specifically if running in a minimalist shoe replicates barefoot running. Methods Ground reaction force data and kinematics were collected from 22 highly trained runners during overground running while barefoot and in three shod conditions (minimalist shoe, racing flat and the athlete's regular shoe). Three-dimensional net joint moments and subsequent net powers and work were computed using Newton-Euler inverse dynamics. Joint kinematic and kinetic variables were statistically compared between barefoot and shod conditions using a multivariate analysis of variance for repeated measures and standardised mean differences calculated. Results There were significant differences between barefoot and shod conditions for kinematic and kinetic variables at the knee and ankle, with no differences between shod conditions. Barefoot running demonstrated less knee flexion during midstance, an 11% decrease in the peak internal knee extension and abduction moments and a 24% decrease in negative work done at the knee compared with shod conditions. The ankle demonstrated less dorsiflexion at initial contact, a 14% increase in peak power generation and a 19% increase in the positive work done during barefoot running compared with shod conditions. Conclusions Barefoot running was different to all shod conditions. Barefoot running changes the amount of work done at the knee and ankle joints and this may have therapeutic and performance implications for runners.

Recent findings suggest that not only the lack of physical activity, but also prolonged times of sedentary behaviour where major locomotor muscles are inactive, significantly increase the risk of chronic diseases. The purpose of this study was to provide details of quadriceps and hamstring muscle inactivity and activity during normal daily life of ordinary people. Eighty-four volunteers (44 females, 40 males, 44.1±17.3 years, 172.3±6.1 cm, 70.1±10.2 kg) were measured during normal daily life using shorts measuring muscle electromyographic (EMG) activity (recording time 11.3±2.0 hours). EMG was normalized to isometric MVC (EMG_MVC) during knee flexion and extension, and inactivity threshold of each muscle group was defined as 90% of EMG activity during standing (2.5±1.7% of EMG_MVC). During normal daily life the average EMG amplitude was 4.0±2.6% and average activity burst amplitude was 5.8±3.4% of EMG_MVC (mean duration of 1.4±1.4 s) which is below the EMG level required for walking (5 km/h corresponding to EMG level of about 10% of EMG_MVC). Using the proposed individual inactivity threshold, thigh muscles were inactive 67.5±11.9% of the total recording time and the longest inactivity periods lasted for 13.9±7.3 min (2.5–38.3 min). Women had more activity bursts and spent more time at intensities above 40% EMG_MVC than men (p<0.05). In conclusion, during normal daily life the locomotor muscles are inactive about 7.5 hours, and only a small fraction of muscle's maximal voluntary activation capacity is used averaging only 4% of the maximal recruitment of the thigh muscles. Some daily non-exercise activities such as stair climbing produce much higher muscle activity levels than brisk walking, and replacing sitting by standing can considerably increase cumulative daily muscle activity.

Purpose Asymmetrical loading patterns are commonplace in football sports. Our aim was to examine the influence of training age and limb function on lower-body musculoskeletal morphology. Methods Fifty-five elite football athletes were stratified into less experienced (≤3 yr; n = 27) and more experienced (>3 yr; n = 28) groups by training age. All athletes underwent whole-body dual-energy x-ray absorptiometry scans and lower-body peripheral quantitative computed tomography tibial scans on the kicking and support limbs. Results Significant interactions between training age and limb function were evident across all skeletal parameters (F16, 91 = 0.182, P = 0.031, Wilks Λ = 0.969). Asymmetries between limbs were significantly larger in the more experienced players than the less experienced players for tibial mass (P ≤ 0.044, d ≥ 0.50), total cross-sectional area (P ≤ 0.039, d ≥ 0.53), and stress–strain indices (P ≤ 0.050, d ≥ 0.42). No significant asymmetry was evident for total volumetric density. More experienced players also exhibited greater lower-body tibial mass (P ≤ 0.001, d ≥ 1.22), volumetric density (P ≤ 0.009, d ≥ 0.79), cross-sectional area (P ≤ 0.387, d ≥ 0.21), stress–strain indices (P ≤ 0.012, d ≥ 0.69), fracture loads (P ≤ 0.018, d ≥ 0.57), and muscle mass and cross-sectional area (P ≤ 0.016, d ≥ 0.68) than less experienced players. Conclusions Asymmetries were evident in athletes as a product of limb function over time. Chronic exposure to routine high-impact gravitational loads afforded to the support limb preferentially improved bone mass and structure (cross-sectional area and cortex thickness) as potent contributors to bone strength relative to the high-magnitude muscular loads predominantly afforded to the kicking limb.

Neural control of muscle contraction seems to be unique during muscle lengthening. The present study aimed to determine the specific sites of modulatory control for lengthening compared with isometric contractions. We used stimulation of the motor cortex and corticospinal tract to observe changes at the spinal and cortical levels. Motor-evoked potentials (MEPs) and cervicomedullary MEPs (CMEPs) were evoked in biceps brachii and brachioradialis during maximal and submaximal lengthening and isometric contractions at the same elbow angle. Sizes of CMEPs and MEPs were lower in lengthening contractions for both muscles (by ∼28 and ∼16%, respectively; P < 0.01), but MEP-to-CMEP ratios increased (by ∼21%; P < 0.05). These results indicate reduced excitability at the spinal level but enhanced motor cortical excitability for lengthening compared with isometric muscle contractions.