Key points: Goal‐directed arm movements can be adjusted at short latency to target shifts. We tested whether similar adjustments are present during walking on a treadmill with shifting stepping targets. Participants responded at short latency with an adequate gain to small shifts of the stepping targets. Movements of the feet during walking are controlled in a similar way to goal‐directed arm movements if balance is not violated. It is well‐known that goal‐directed hand movements can be adjusted to small changes in target location with a latency of about 100 ms. We tested whether people make similar fast adjustments when a target location for foot placement changes slightly as they walk over a flat surface. Participants walked at 3 km/h on a treadmill on which stepping stones were projected. The stones were 50 cm apart in the walking direction. Every 5–8 steps, a stepping stone was unexpectedly displaced by 2.5 cm in the medio‐lateral direction. The displacement took place during the first half of the swing phase. We found fast adjustments of the foot trajectory, with a latency of about 155 ms, initiated by changes in muscle activation 123 ms after the perturbation. The responses corrected for about 80% of the perturbation. We conclude that goal‐directed movements of the foot are controlled in a similar way to those of the hand, thus also giving very fast adjustments.

When reaching towards an object while standing, one’s hand responds very quickly to visual perturbations such as the target being displaced or the background moving. Such responses require postural adjustments. When the background moves, its motion might be attributed to self-motion in a stable world, and thereby induce compensatory postural adjustments that affect the hand. The changes in posture associated with a given hand movement response may, therefore, be different for the two types of perturbations. To see whether they are, we asked standing participants to move their hand in the sagittal direction away from their body to targets displayed on a horizontal screen in front of them. The target displacements and background motion were in the lateral direction. We found hand movement responses that were in line with earlier reports, with a latency that was slightly shorter for target displacements than for background motion, and that was independent of target displacement size or background motion speed. The trunk responded to both perturbations with a modest lateral sway. The two main findings were that the upper trunk responded even before the hand did so and that the head responded to background motion but hardly responded to target displacements. These findings suggest that postural adjustments associated with adjusting the hand movement precede the actual adjustments to the movement of the hand, while at the same time, participants try to keep their head stable on the basis of visual information.

Purpose: Human sensory and motor systems deteriorate with age. When walking, older adults may therefore find it more difficult to adjust their steps to new visual information, especially considering that such adjustments require control of balance as well as of foot trajectory. Our study investigates the effects of ageing on lower limb responses to unpredictable target shifts. Methods: Participants walked on a treadmill with projected stepping targets that occasionally shifted in the medial or lateral direction. The shifts occurred at a random moment during the early half of the swing phase of either leg. Kinematic, kinetic and muscle activity data were collected. Results: Older adults responded later and corrected for a smaller proportion of the shift than young adults. The order in which muscle activation changed was similar in both groups, with responses of gluteus medius and semitendinosus from about 120 to 140 ms after the shift. Most muscles responded slightly later to lateral target shifts in the older adults than in the young adults, but this difference was not observed for medial target shifts. Ageing delayed the behavioural responses more than it did the electromyographic (EMG) responses. Conclusions: Our study suggests that older adults can adjust their walking to small target shifts during the swing phase, but not as well as young adults. Furthermore, muscle strength probably plays a substantial role in the changes in online adjustments during ageing.

People can quickly adjust their goal-directed hand movements to an unexpected visual perturbation (a target jump or background motion). Does this ability decrease with age? We examined how aging affects both the timing and vigor of fast manual and postural adjustments to visual perturbations. Young and older adults stood in front of a horizontal screen. They were instructed to tap on targets presented on the screen as quickly and accurately as possible by moving their hand in the sagittal direction. In some trials, the target or the background moved laterally when the hand started to move. The young and older adults tapped equally accurately, but older adults’ movement times were about 160 ms longer. The manual responses were similar for the young and older adults, but the older adults took about 15 ms longer to respond to both kinds of visual perturbations. The manual responses were also less vigorous for the older adults. In contrast to the young adults, the older adults responded more strongly to the motion of the background than to the target jump, probably because the elderly rely more on visual information for their posture. Thus, aging delays responses to visual perturbations, while at the same time making people rely more on the visual surrounding to adjust goal-directed movements.

Background and Objectives: Recent studies have shown that low skeletal muscle mass can contribute to non-alcoholic fatty liver disease through insulin resistance. However, the association between muscle mass/strength and hepatic fat content remains unclear in postmenopausal women. Methods: In this study, we assessed the associations between muscle mass/strength and various severities of non-alcoholic fatty liver disease. Using single-voxel proton magnetic resonance spectroscopy, 96 postmenopausal women between the ages of 50 and 65 were divided into four groups (G0–G3) by hepatic fat content: G0 (hepatic fat content <5%, n = 20), G1 (5% ≤ hepatic fat content < 10%, n = 27), G2 (10% ≤ hepatic fat content < 25%, n = 31), and G3 (hepatic fat content ≥25%, n = 18). Muscle mass indexes were estimated as skeletal muscle index (SMI)% (total lean mass/weight × 100) and appendicular skeletal muscular mass index (ASM)% (appendicular lean mass/weight × 100) by dual energy X-ray absorptiometry. Maximal isometric voluntary contraction of the handgrip, elbow flexors, and knee extensors was measured using an adjustable dynamometer chair. Fasting plasma glucose, insulin, and follicle-stimulating hormones were assessed in venous blood samples. Results: The results showed negative correlations between hepatic fat content and SMI% (r = −0.42, p < 0.001), ASM% (r = −0.29, p = 0.005), maximal voluntary force of grip (r = −0.22, p = 0.037), and knee extensors (r = −0.22, p = 0.032). Conclusions: These significant correlations almost remained unchanged even after controlling for insulin resistance. In conclusion, negative correlations exist between muscle mass/strength and the progressed severity of non-alcoholic fatty liver disease among post-menopausal women, and the correlations are independent of insulin resistance.

If the surrounding of a visual target unexpectedly starts to move during a fast goal-directed hand movement, the hand reflexively moves along with it. This is known as the ‘manual following response’. One explanation for this response is that it is a compensation for inferred self-motion in space. Previous studies have shown that background motion gives rise to both postural responses and deviations in goal-directed hand movements. To evaluate whether compensation for inferred self-motion is responsible for the manual responses we examined whether galvanic stimulation of the vestibular system would give rise to similar deviations in hand movements. Standing participants tried to quickly tap on targets that were presented on a horizontal screen. Participants could infer self-motion on some of the trials, either from galvanic vestibular stimulation or from background motion. Both perturbations took place during the hand movement. It took both the head and hand about 45 ms longer to respond to background motion than to respond to galvanic stimulation. The head responded in a similar manner to both types of perturbations. The hand responded about as expected to galvanic stimulation, but much more vigorously to background motion. Thus, the manual response to background motion is probably not a direct consequence of trying to compensate for inferred self-motion. Perhaps the manual following response is a consequence of an error in binding motion information to objects.