The Combined Effects of Body Weight Support and Gait Speed on Gait Related Muscle Activity: A Comparison between Walking in the Lokomat Exoskeleton and Regular Treadmill Walking

Background

For the development of specialized training protocols for robot assisted gait training, it is important to understand how the use of exoskeletons alters locomotor task demands, and how the nature and magnitude of these changes depend on training parameters. Therefore, the present study assessed the combined effects of gait speed and body weight support (BWS) on muscle activity, and compared these between treadmill walking and walking in the Lokomat exoskeleton.

Methods

Ten healthy participants walked on a treadmill and in the Lokomat, with varying levels of BWS (0% and 50% of the participants’ body weight) and gait speed (0.8, 1.8, and 2.8 km/h), while temporal step characteristics and muscle activity from Erector Spinae, Gluteus Medius, Vastus Lateralis, Biceps Femoris, Gastrocnemius Medialis, and Tibialis Anterior muscles were recorded.

Results

The temporal structure of the stepping pattern was altered when participants walked in the Lokomat or when BWS was provided (i.e. the relative duration of the double support phase was reduced, and the single support phase prolonged), but these differences normalized as gait speed increased. Alternations in muscle activity were characterized by complex interactions between walking conditions and training parameters: Differences between treadmill walking and walking in the exoskeleton were most prominent at low gait speeds, and speed effects were attenuated when BWS was provided.

Conclusion

Walking in the Lokomat exoskeleton without movement guidance alters the temporal step regulation and the neuromuscular control of walking, although the nature and magnitude of these effects depend on complex interactions with gait speed and BWS. If normative neuromuscular control of gait is targeted during training, it is recommended that very low speeds and high levels of BWS should be avoided when possible.     

A New Approach to the Analysis of Normal Muscle Electrical Activity during Walking in Humans

Introduction of short-term disturbances into the biomechanical structure of the human gait with simultaneous recording of the muscle electrical activity has been used to demonstrate that the human body has an intraspinal locomotor program consisting of an inhibition period, when afferent stimuli cause no response, and an excitation period, when the responses are expressed. The electromyographic profile of the leg muscles of subjects walking on a horizontal surface, up stairs, and down stairs may be divided into three zones. The H and M zones (the highest and moderate activities, respectively) correspond to the centrally programmed excitation period, and the L zone (low-amplitude activity), to the centrally programmed inhibition period. The difference between the former two zones is that the activity in the H zone is regular, whereas the M-zone activity is irregular and varies depending on biomechanical conditions. Apparently, the steady activity in the H zone is determined by the combined effect of the spinal generator of locomotion movements, cyclic supraspinal stimuli, and various (mainly proprioceptive) afferent impulses from the leg. An increase in the M-zone activity is mainly determined by afferent stimuli.     

Nordic Walking improves daily physical activities in COPD: a randomised controlled trial

Background

In patients with COPD progressive dyspnoea leads to a sedentary lifestyle. To date, no studies exist investigating the effects of Nordic Walking in patients with COPD. Therefore, the aim was to determine the feasibility of Nordic Walking in COPD patients at different disease stages. Furthermore we aimed to determine the short- and long-term effects of Nordic Walking on COPD patients'' daily physical activity pattern as well as on patients exercise capacity.

Methods

Sixty COPD patients were randomised to either Nordic Walking or to a control group. Patients of the Nordic Walking group (n = 30; age: 62 ± 9 years; FEV₁: 48 ± 19% predicted) underwent a three-month outdoor Nordic Walking exercise program consisting of one hour walking at 75% of their initial maximum heart rate three times per week, whereas controls had no exercise intervention. Primary endpoint: daily physical activities (measured by a validated tri-axial accelerometer); secondary endpoint: functional exercise capacity (measured by the six-minute walking distance; 6MWD). Assessment time points in both groups: baseline, after three, six and nine months.

Results

After three month training period, in the Nordic Walking group time spent walking and standing as well as intensity of walking increased (Δ walking time: +14.9 ± 1.9 min/day; Δ standing time: +129 ± 26 min/day; Δ movement intensity: +0.40 ± 0.14 m/s²) while time spent sitting decreased (Δ sitting time: -128 ± 15 min/day) compared to baseline (all: p < 0.01) as well as compared to controls (all: p < 0.01). Furthermore, 6MWD significantly increased compared to baseline (Δ 6MWD: +79 ± 28 meters) as well as compared to controls (both: p < 0.01). These significant improvements were sustained six and nine months after baseline. In contrast, controls showed unchanged daily physical activities and 6MWD compared to baseline for all time points.

Conclusions

Nordic Walking is a feasible, simple and effective physical training modality in COPD. In addition, Nordic Walking has proven to positively impact the daily physical activity pattern of COPD patients under short- and long-term observation.

Clinical trial registration

Nordic Walking improves daily physical activities in COPD: a randomised controlled trial - ISRCTN31525632     

Correlation between Muscle Strength and Muscle Mass,and Their Association with Walking Speed,in Community-Dwelling Elderly Japanese Individuals

Objectives

We aimed to assess the correlation between muscle strength and muscle mass based on sex and age, and their association with walking speed, which is a health predictor for independent living, in elderly Japanese individuals.

Methods

The participants included 318 (111 men, 207 women) community-dwelling elderly Japanese individuals aged ≥65 years. Knee extension strength was assessed as an indicator of muscle strength, and bioelectrical impedance analysis was used to measure muscle mass. The maximum walking speed of participants was recorded. All measurements were categorized based on sex and age groups as follows: young-old (age, 65–74 years) and old-old (age, ≥75 years).

Results

Appendicular muscle mass and knee extension strength decreased with age in both men and women. In men, knee extension strength showed significant positive correlations with leg and appendicular muscle mass in both young-old and old-old age groups. However, in women, only the old-old age group showed significant positive correlations between knee extension strength and leg and appendicular muscle mass. Muscle strength was significantly positively correlated with maximum walking speed in all groups, whereas muscle mass was not significantly correlated with maximum walking speed in men and women.

Conclusions

Muscle strength was significantly correlated with muscle mass in both age groups in men. However, in women, the correlation between muscle strength and muscle mass differed according to age. This finding suggests that the relationship between muscle strength and muscle mass differs according to sex and age. Muscle strength showed significant correlation with walking speed in both men and women in both age groups. These findings suggest that it is necessary to recognize that muscle strength is different from muscle mass, and that an individualized approach to prevent decline of muscle strength and muscle mass is necessary for health promotion in elderly.     

Comparison of Trunk Activity during Gait Initiation and Walking in Humans

To understand the role of trunk muscles in maintenance of dynamic postural equilibrium we investigate trunk movements during gait initiation and walking, performing trunk kinematics analysis, Erector spinae muscle (ES) recordings and dynamic analysis. ES muscle expressed a metachronal descending pattern of activity during walking and gait initiation. In the frontal and horizontal planes, lateroflexion and rotation occur before in the upper trunk and after in the lower trunk. Comparison of ES muscle EMGs and trunk kinematics showed that trunk muscle activity precedes corresponding kinematics activity, indicating that the ES drive trunk movement during locomotion and thereby allowing a better pelvis mobilization. EMG data showed that ES activity anticipates propulsive phases in walking with a repetitive pattern, suggesting a programmed control by a central pattern generator. Our findings also suggest that the programs for gait initiation and walking overlap with the latter beginning before the first has ended.     

Walking strategies during the transition between level and hill surfaces

Healthy young adults transition between level and hill surfaces of various angles while walking at fluctuating speeds. These surface transitions have the potential to decrease dynamic balance in both the anterior-posterior and medial-lateral directions. Hence, the purpose of the current study was to analyze modifications in temporal-spatial parameters during hill walking transitions. We hypothesized that in comparison with level walking, the transition strides would indicate the adoption of a distinct gait strategy with a greater base of support. Thirty-four participants completed level and hill trials on a walkway with a 15-degree portable ramp apparatus. We collected data during 4 transition strides between level and ramp surfaces. In support of our hypothesis, compared with level walking, the base of support was 20% greater during 3 out of the 4 transition strides. In short, our results illustrate that healthy young adults did adopt a distinct gait strategy different from both level and hill walking during transitions strides.     

Dual Regulation of Muscle Glycogen Synthase during Exercise by Activation and Compartmentalization

Glycogen synthase (GS) is considered the rate-limiting enzyme in glycogenesis but still today there is a lack of understanding on its regulation. We have previously shown phosphorylation-dependent GS intracellular redistribution at the start of glycogen re-synthesis in rabbit skeletal muscle (Prats, C., Cadefau, J. A., Cussó, R., Qvortrup, K., Nielsen, J. N., Wojtaszewki, J. F., Wojtaszewki, J. F., Hardie, D. G., Stewart, G., Hansen, B. F., and Ploug, T. (2005) J. Biol. Chem. 280, 23165–23172). In the present study we investigate the regulation of human muscle GS activity by glycogen, exercise, and insulin. Using immunocytochemistry we investigate the existence and relevance of GS intracellular compartmentalization during exercise and during glycogen re-synthesis. The results show that GS intrinsic activity is strongly dependent on glycogen levels and that such regulation involves associated dephosphorylation at sites 2+2a, 3a, and 3a + 3b. Furthermore, we report the existence of several glycogen metabolism regulatory mechanisms based on GS intracellular compartmentalization. After exhausting exercise, epinephrine-induced protein kinase A activation leads to GS site 1b phosphorylation targeting the enzyme to intramyofibrillar glycogen particles, which are preferentially used during muscle contraction. On the other hand, when phosphorylated at sites 2+2a, GS is preferentially associated with subsarcolemmal and intermyofibrillar glycogen particles. Finally, we verify the existence in human vastus lateralis muscle of the previously reported mechanism of glycogen metabolism regulation in rabbit tibialis anterior muscle. After overnight low muscle glycogen level and/or in response to exhausting exercise-induced glycogenolysis, GS is associated with spherical structures at the I-band of sarcomeres.The desire to understand metabolism and its regulation dates back several centuries, but it has exponentially increased during the last decades in an effort to treat or prevent type 2 diabetes mellitus (T2DM).3 Defective muscle glycogen synthesis has been repeatedly reported in patients with T2DM (1–3). Several studies have shown impairments of insulin-induced glycogen synthase (GS) activation in skeletal muscle from T2DM patients and in healthy subjects at increased risk for T2DM, such as healthy obese and first-degree relatives of patients with T2DM (4–9).The first scientific studies on GS date from the 1960s, but still today there is a lack of understanding on its regulation. GS is the rate-limiting enzyme in glycogenesis and is classically used as an example of an allosterically and covalently regulated enzyme. It is well accepted that GS is complexly regulated by sequences of hierarchal phosphorylations (10) in at least nine sites and by its allosteric activator, glucose 6-phosphate (G6P) (11, 12). However, the exact effects of GS phosphorylation at different sites on its regulation are still not clear. GS phosphorylation sites are distributed between the NH₂- and the COOH-terminal domains. The NH₂ terminus domain contains two sites, 2 (Ser⁷) and 2a (Ser¹⁰), that are phosphorylated in a hierarchal mode. Phosphorylation of site 2 is needed as a recognition motif for casein kinase 1 to phosphorylate site 2a (13, 14). Several protein kinases have been reported to phosphorylate site 2 in vitro, among them PKA, CaMKII, PKC, AMPK, GPhK, and MAPKAPKII (15–17). At the COOH terminus of muscle GS, there are at least seven phosphorylation sites; sites 3a (Ser⁶⁴⁰), 3b (Ser⁶⁴⁴), 3c (Ser⁶⁴⁸), 4 (Ser⁶⁵²), 5 (Ser⁶⁵⁶), 1a (Ser⁶⁹⁷), and 1b (Ser⁷¹⁰). Sites 3, 4, and 5 are phosphorylated in a hierarchal mode. Casein kinase II phosphorylates site 5, establishing a recognition motif for GSK-3 to phosphorylate sequentially sites 4, 3c, 3b, and 3a (18–21). Dephosphorylation of sites 2 and 3 increase GS intrinsic activity much more than dephosphorylation of the remaining sites, which have little or no effect on the enzyme activity (22). The effect of GS phosphorylation at sites 1a and 1b remains elusive. G6P binding reverses covalent inactivation of GS by phosphorylation (11) and increases susceptibility of the enzyme to be activated by the action of protein phosphatases (23), mainly by glycogen-targeted protein phosphatase 1.Intracellular compartmentalization of GS has been reported in several studies. In isolated hepatocytes, incubation with glucose induces GS activation and intracellular translocation to the cell periphery (24). In contrast, in the absence of glucose, GS has been shown to be mainly located inside the nucleus of both cultured liver and muscle cells; however, following addition of glucose GS translocates to the cytosol (25). In a previous study, we reported a novel regulatory mechanism of skeletal muscle glycogen metabolism (26). We showed that severe glycogen depletion induced by muscle contraction leads to rearrangement of cytoskeleton actin filaments to form dynamic intracellular compartments. Both GS and phosphorylase associate with such compartments to start glycogen re-synthesis. Furthermore, we showed that GS phosphorylated at site 1b (P-GS1b) was located at the cross-striations, the I-band of sarcomeres, whereas when phosphorylated at sites 2+2a (P-GS2+2a), GS formed some clusters homogeneously distributed along muscle fibers. In the present study we investigate the existence and relevance of such regulatory mechanism in human muscle metabolism.     

Neuromuscular Activation of the Vastus Intermedius Muscle during Isometric Hip Flexion

Although activity of the rectus femoris (RF) differs from that of the other synergists in quadriceps femoris muscle group during physical activities in humans, it has been suggested that the activation pattern of the vastus intermedius (VI) is similar to that of the RF. The purpose of present study was to examine activation of the VI during isometric hip flexion. Ten healthy men performed isometric hip flexion contractions at 25%, 50%, 75%, and 100% of maximal voluntary contraction at hip joint angles of 90°, 110° and 130°. Surface electromyography (EMG) was used to record activity of the four quadriceps femoris muscles and EMG signals were root mean square processed and normalized to EMG amplitude during an isometric knee extension with maximal voluntary contraction. The normalized EMG was significantly higher for the VI than for the vastus medialis during hip flexion at 100% of maximal voluntary contraction at hip joint angles of 110° and 130° (P < 0.05). The onset of VI activation was 230–240 ms later than the onset of RF activation during hip flexion at each hip joint angle, which was significantly later than during knee extension at 100% of maximal voluntary contraction (P < 0.05). These results suggest that the VI is activated later than the RF during hip flexion. Activity of the VI during hip flexion might contribute to stabilize the knee joint as an antagonist and might help to smooth knee joint motion, such as in the transition from hip flexion to knee extension during walking, running and pedaling.     

Inter-relationships between pituitary-adrenal hormones and catecholamines during a 6-day Nordic ski race

The aim of the study was to investigate the inter-relationships between pituitary-adrenal hormones and catecholamines during a prolonged competition over 6 days. Plasma adrenocorticotropic hormone (ACTH), cortisol (C), beta-endorphin (beta EP), free and sulphated adrenaline (A) and noradrenaline (NA) were measured in 11 volunteer male subjects during a national Nordic-ski race (323 km). Blood samples were obtained before the competition in the evening as control (D0), and before and after each day's racing (D1-D6). The mean daily heart rate (fc) was calculated from fc values recorded every minute during the race. The results showed the following: changes in mean fc [from 147 (SEM 3) to 156 (SEM 3) beats.min-1 according to the day] were not significant during the race. Diurnal variations in ACTH, beta EP and C were no longer apparent after the race: evening levels were higher than their respective D0 values during the race, except on D3 when there was a lack of response to exercise in the three hormones. Unlike ACTH and beta EP, pre- and postexercise C values on D1 and D2 were higher than those on the subsequent days (P less than 0.001). In contrast, there was a progressive accumulation of A and NA in pre- and postrace concentrations which reached a plateau in about 4 days. Positive correlations between exercise responses in ACTH, C and beta EP were found especially on D3 and D6 (P less than 0.001) but there were no significant correlations between catecholamines and the other three hormones. Thus, prolonged competition over 6 days evoked different control mechanisms for hormones of the pituitary-adrenal axis and catecholamines.(ABSTRACT TRUNCATED AT 250 WORDS)     

AMP-activated Protein Kinase Stimulates Warburg-like Glycolysis and Activation of Satellite Cells during Muscle Regeneration

Satellite cells are the major myogenic stem cells residing inside skeletal muscle and are indispensable for muscle regeneration. Satellite cells remain largely quiescent but are rapidly activated in response to muscle injury, and the derived myogenic cells then fuse to repair damaged muscle fibers or form new muscle fibers. However, mechanisms eliciting metabolic activation, an inseparable step for satellite cell activation following muscle injury, have not been defined. We found that a noncanonical Sonic Hedgehog (Shh) pathway is rapidly activated in response to muscle injury, which activates AMPK and induces a Warburg-like glycolysis in satellite cells. AMPKα1 is the dominant AMPKα isoform expressed in satellite cells, and AMPKα1 deficiency in satellite cells impairs their activation and myogenic differentiation during muscle regeneration. Drugs activating noncanonical Shh promote proliferation of satellite cells, which is abolished because of satellite cell-specific AMPKα1 knock-out. Taken together, AMPKα1 is a critical mediator linking noncanonical Shh pathway to Warburg-like glycolysis in satellite cells, which is required for satellite activation and muscle regeneration.     

Walking Performance: Correlation between Energy Cost of Walking and Walking Participation. New Statistical Approach Concerning Outcome Measurement

Walking ability, though important for quality of life and participation in social and economic activities, can be adversely affected by neurological disorders, such as Spinal Cord Injury, Stroke, Multiple Sclerosis or Traumatic Brain Injury. The aim of this study is to evaluate if the energy cost of walking (CW), in a mixed group of chronic patients with neurological diseases almost 6 months after discharge from rehabilitation wards, can predict the walking performance and any walking restriction on community activities, as indicated by Walking Handicap Scale categories (WHS). One hundred and seven subjects were included in the study, 31 suffering from Stroke, 26 from Spinal Cord Injury and 50 from Multiple Sclerosis. The multivariable binary logistical regression analysis has produced a statistical model with good characteristics of fit and good predictability. This model generated a cut-off value of.40, which enabled us to classify correctly the cases with a percentage of 85.0%. Our research reveal that, in our subjects, CW is the only predictor of the walking performance of in the community, to be compared with the score of WHS. We have been also identifying a cut-off value of CW cost, which makes a distinction between those who can walk in the community and those who cannot do it. In particular, these values could be used to predict the ability to walk in the community when discharged from the rehabilitation units, and to adjust the rehabilitative treatment to improve the performance.     

A Comparison of Walking Rates Between Wild and Zoo African Elephants

With increased scrutiny surrounding the welfare of elephants in zoological institutions, it is important to have empirical evidence on their current welfare status. If elephants are not receiving adequate exercise, it could lead to obesity, which can lead to many issues including acyclicity and potentially heart disease. The goal of the current study was to compare the walking rates of elephants in the wild versus elephants in zoos to determine if elephants are walking similar distances relative to their wild counterparts. Eleven wild elephants throughout different habitats and locations in Botswana were compared to 8 elephants at the San Diego Zoo Safari Park. Direct comparisons revealed no significant difference in average walking rates of zoo elephants when compared with wild elephants. These results suggest that elephants at the San Diego Zoo Safari Park walk similar rates to those of wild elephants and may be meeting their exercise needs.     

无痛胃肠镜与常规胃肠镜在消化道疾病诊治中的临床对比分析

目的:探究并分析无痛胃肠镜与常规胃肠镜在消化道疾病诊治中的临床应用价值。方法:于2014年5月~2015年5期间,选择我院收治的胃肠消化道疾病患者64例为研究对象,根据患者对胃肠镜检测方式的选择,将其分为研究组(33例)和对照组(31例)。研究组患者给予无痛胃肠镜检查,对照组给予常规胃肠镜检查,观察并记录两组患者胃肠镜检查前后血氧饱和度(SpO_2)、心率及血压的变化,内镜操作过程中咽喉反射发生率、不良反应的发生率,术后内镜检查效果评价及患者对操作的满意度。结果:研究组胃肠镜检查效果显著优于对照组,且研究组优良率显著高于对照组(P0.05);研究组患者在胃肠镜检查前后心率、血压及SpO_2均未出现明显变化(P0.05),而对照组患者在内镜查前后心率、血压均出现明显变化,术中心率、血压均明显高于术前和术后(P0.05);研究组患者出现咽喉反射及不良反应发生率均显著低于对照组,对操作满意度显著高于对照组(P0.05)。结论:无痛胃肠镜与常规胃肠镜相比,患者适应性更好、疼痛轻、不良反应少、安全性高,且患者对操作的满意度高。     

大鼠与家兔生后各年龄阶段跖肌纤维的比较

应用建立在肌球蛋白重链异构体基础上的标准肌动球蛋白ATP酶和琥珀酸脱氢酶组织化学方法,分析大鼠和家兔出生后发育各年龄阶段跖肌纤维型分布。在生后2周至24周龄的大鼠和家兔Ⅰ、ⅡX型肌纤维百分比例减少,而ⅡA、ⅡB型纤维则增加。进行大量单肌纤维的组织化学特征的比较和相关性探讨。结果显示动物平均体重与跖肌的平均湿重随生后发育逐渐增加,Ⅰ、ⅡX、ⅡA及ⅡB型纤维均在生后各年龄组的全部肌肉内被发现,但出生后2日龄组是个例外。在生后发育期间,雄性大鼠和家兔ⅡB型纤维的平均肌纤维型构成要大于雌性大鼠和家兔,而雄性大鼠和家兔Ⅰ、ⅡX、ⅡA型三种氧化组织化学分类的肌纤维型构成均小于雌性大鼠和家兔。大鼠Ⅰ、ⅡX、ⅡA和ⅡB型纤维的平均横切面积显然要比家兔的同类型肌纤维要小。在大鼠和家兔可见明显的性别差异。大鼠和家兔的ⅡX型纤维横切面积是最小的,Ⅰ、ⅡA型纤维呈中等大小,ⅡB型纤维最大。该重要的测试有助于我们深入研究啮齿类动物快肌纤维生理特征的适应。     

Cerium-Based Demonstration of Phosphatas Activity in Plastic-Embedded Sections: A Comparison with Conventional Methods

Cerium-based methods have been used for the demonstration of seve phatases at alkaline, acid and neutral pH in low temperature acetone-fixed, plastic-e sections. At alkaline pH calcium is used as capturing agent and the precipitated phosphate converted to cerium phosphate. At neutral and acid pH cerium is used d capturing agent. Cerium phosphate is subsequently visualized using the H₂C₂DAB n: comparison has been made with conventional calcium-cobalt and lead methods. It; that calcium-cobalt methods are more susceptible to improvement than lead methods