The Exercise-Cholesterol Link
Continued But even walking may be too much for someone who is overweight and has joint pain. Our research has led to breakthroughs in treatment and improved care that bring hope to the entire Parkinson's community. Ajzlab, March 8, But to avoid knee strain, you must make sure the bike is adjusted to fit your body, Vukovich says. You can perform this simple strength training routine from your living room. Any vegetable juice that does not have a lot of added sugar, corn syrup, etc. Leptin has thus emerged as a candidate to link obesity and osteoarthritis and serves as an apparent objective as a nutritional treatment for osteoarthritis.
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When it comes to fat loss, slow and steady loses the race. More intense training -- in shorter bursts -- burns calories more quickly and burns more fat overall. And unlike long, slow cardio sessions, intense training keeps you melting fat even after your workout is over, says Martin Rooney, director of the Parisi Speed School and author of "Ultimate Warrior Workouts. For fat loss, the two best exercises to eliminate from your routine, says Ballantyne, are "the fork to mouth and the ounce curl.
Put down the tortilla chips, and try these five high-intensity training strategies to torch fat fast. Men and women who did hours of cardio over the course of a year lost an average of only five pounds.
Interval training -- bouts of high-intensity exercise alternated with short rest periods -- not only burns more calories than traditional cardio training, but also boosts your body's ability to fry fat through hormone production. Not only are interval workouts shorter than traditional cardio training, but they also make you fitter in fewer sessions, he adds. Steady-state works by increasing the oxygen delivery to your heart and lungs. Intervals, however, work on your muscles, helping them use oxygen more efficiently so your heart doesn't have to pump as much to make them perform.
Jump on a stationary bike or onto a treadmill, and start your own interval training regimen with this guide from Ballantyne:. Start with a regular warmup. When you've finished that, pedal or run at a rate that's 20 percent harder than your normal cardio intensity. After 30 to 60 seconds, bring the intensity down to a rate that's half the intensity of a normal cardio workout. You want two extremes: Alternate periods of 30 to 60 seconds of hard work with 30 to 60 seconds of easy pedaling or easy running for six to 10 intervals to complete your session.
As this gets easier, increase the intensity of each interval, work longer during the hard portion, shorten your rest periods or add more intervals. If you haven't sprinted since a coach was blasting a whistle in your ear, you're missing out on a natural but extreme form of interval training that can pay dividends for more than just your legs. They have tremendous arms and shoulders, too," said Nick Tumminello, director of Performance University.
A quick caveat, though: If you're not used to bursts like these, Tumminello says, it's easy to pull a hamstring, halting your training -- and your results.
He suggests following these tips to start safely. Sprint on a hill. The impact on your joints is lower, Tumminello says, which can help you avoid injury. Live in a flat area with no hills? Instead of the drag race approach, begin your sprints by speeding up from a jog. At a local track, jog the curve, then sprint 10 to 20 yards of the straightaway. Continue interval sprinting in this way. To maximize benefit and lower injury risk, keep your sprints on the shorter side -- no more than 50 yards per sprint.
This will help you maintain a high intensity throughout, says Tumminello, and prevent your form from breaking down, which can lead to injury. To increase the overall results of your sprint workout, increase the number of sprints instead of going for long distances.
When you're starting out, perform a sprint workout just once per week -- you'll be surprised at how sore the workout makes you, even in the abdominals. Once you're used to the stimulus, Tumminello suggests bumping it up to only two sessions per week, mixed with other gym workouts.
Allow at least two days of recovery between sprint workouts. You don't have to run, bike or perform any traditional cardio exercise to get high-intensity, fat-burning training. By pairing strength exercises that work opposing muscles, you can build muscle while keeping your heart rate high, maximizing fat loss. During the lunges, the arms and back rest, while the legs rest during the pull-ups. Jack uses such exercise pairings to do escalating density training, an interval protocol with a built-in challenge.
To try this challenge: Choose two exercises that use opposite movements or work completely different muscles -- pair a pushing exercise with a pulling exercise or a lower body move with an upper body move. As an example, consider a dumbbell bench press and an inverted row. For each exercise, choose a weight with which you can perform 10 reps. Alternate between the exercises, performing just five reps of each move, with the rep weight, in each set.
Rest as needed between sets and pairs so that you can complete each set of five without failing. As with cardio intervals, strength intervals like these won't work if your reps aren't high-intensity.
Continue alternating between the exercises for a set time -- 10 or 15 minutes, for example -- keeping track of how many total sets you can do. In following sessions, try to beat your score by finishing more sets in that time or by finishing the same number of sets but with tougher weights. Density training sessions are great to add to the end of a traditional strength training workout, Jack says.
Leptin circulates in blood in free form and bound to proteins. Leptin levels vary exponentially, not linearly, with fat mass. In humans, many instances are seen where leptin dissociates from the strict role of communicating nutritional status between body and brain and no longer correlates with body fat levels:.
All known leptin mutations except one are associated with low to undetectable immunoreactive leptin blood levels. The exception is a mutant leptin reported in January which is not functional, but is detected with standard immunoreactive methods. Predominantly, the "energy expenditure hormone" leptin is made by adipose cells , thus it is labeled fat cell-specific.
In the context of its effects , it is important to recognize that the short describing words direct , central , and primary are not used interchangeably. In regard to the hormone leptin, central vs peripheral refers to the hypothalamic portion of the brain vs non-hypothalamic location of action of leptin; direct vs indirect refers to whether there is no intermediary, or there is an intermediary in the mode of action of leptin; and primary vs secondary is an arbitrary description of a particular function of leptin.
In vertebrates, the nervous system consists of two main parts, the central nervous system CNS and the peripheral nervous system PNS. The primary effect of leptins is in the hypothalamus , a part of the central nervous system.
Leptin receptors are expressed not only in the hypothalamus but also in other brain regions, particularly in the hippocampus. Thus some leptin receptors in the brain are classified as central hypothalamic and some as peripheral non-hypothalamic.
Generally, leptin is thought to enter the brain at the choroid plexus , where the intense expression of a form of leptin receptor molecule could act as a transport mechanism.
Increased levels of melatonin causes a downregulation of leptin,  however, melatonin also appears to increase leptin levels in the presence of insulin , therefore causing a decrease in appetite during sleeping.
Mice with type 1 diabetes treated with leptin or leptin plus insulin, compared to insulin alone had better metabolic profiles: Leptin acts on receptors in the lateral hypothalamus to inhibit hunger and the medial hypothalamus to stimulate satiety. Thus, a lesion in the lateral hypothalamus causes anorexia due to a lack of hunger signals and a lesion in the medial hypothalamus causes excessive hunger due to a lack of satiety signals.
The absence of leptin or its receptor leads to uncontrolled hunger and resulting obesity. Fasting or following a very-low-calorie diet lowers leptin levels.
Leptin binds to neuropeptide Y NPY neurons in the arcuate nucleus in such a way as to decrease the activity of these neurons. Leptin signals to the hypothalamus which produces a feeling of satiety. Moreover, leptin signals may make it easier for people to resist the temptation of foods high in calories. The NPY neurons are a key element in the regulation of hunger; small doses of NPY injected into the brains of experimental animals stimulates feeding, while selective destruction of the NPY neurons in mice causes them to become anorexic.
Once leptin has bound to the Ob-Rb receptor, it activates the stat3, which is phosphorylated and travels to the nucleus to effect changes in gene expression, one of the main effects being the down-regulation of the expression of endocannabinoids , responsible for increasing hunger. It modulates the immune response to atherosclerosis, of which obesity is a predisposing factor. Exogenous leptin can promote angiogenesis by increasing vascular endothelial growth factor levels.
Hyperleptinemia produced by infusion or adenoviral gene transfer decreases blood pressure in rats. Leptin microinjections into the nucleus of the solitary tract NTS have been shown to elicit sympathoexcitatory responses, and potentiate the cardiovascular responses to activation of the chemoreflex.
In fetal lung, leptin is induced in the alveolar interstitial fibroblasts "lipofibroblasts" by the action of PTHrP secreted by formative alveolar epithelium endoderm under moderate stretch. The leptin from the mesenchyme, in turn, acts back on the epithelium at the leptin receptor carried in the alveolar type II pneumocytes and induces surfactant expression, which is one of the main functions of these type II pneumocytes. In mice, and to a lesser extent in humans, leptin is required for male and female fertility.
Ovulatory cycles in females are linked to energy balance positive or negative depending on whether a female is losing or gaining weight and energy flux how much energy is consumed and expended much more than energy status fat levels. When energy balance is highly negative meaning the woman is starving or energy flux is very high meaning the woman is exercising at extreme levels, but still consuming enough calories , the ovarian cycle stops and females stop menstruating.
Only if a female has an extremely low body fat percentage does energy status affect menstruation. Leptin levels outside an ideal range may have a negative effect on egg quality and outcome during in vitro fertilization.
The placenta produces leptin. Leptin is also expressed in fetal membranes and the uterine tissue. Uterine contractions are inhibited by leptin. Immunoreactive leptin has been found in human breast milk; and leptin from mother's milk has been found in the blood of suckling infant animals. Leptin along with kisspeptin controls the onset of puberty.
Leptin's ability to regulate bone mass was first recognized in Leptin decreases cancellous bone , but increases cortical bone. This "cortical-cancellous dichotomy" may represent a mechanism for enlarging bone size, and thus bone resistance, to cope with increased body weight. Bone metabolism can be regulated by central sympathetic outflow, since sympathetic pathways innervate bone tissue. Factors that acutely affect leptin levels are also factors that influence other markers of inflammation, e.
While it is well-established that leptin is involved in the regulation of the inflammatory response,    it has been further theorized that leptin's role as an inflammatory marker is to respond specifically to adipose-derived inflammatory cytokines. In terms of both structure and function, leptin resembles IL-6 and is a member of the cytokine superfamily. Similar to what is observed in chronic inflammation, chronically elevated leptin levels are associated with obesity, overeating, and inflammation-related diseases, including hypertension , metabolic syndrome , and cardiovascular disease.
While leptin is associated with body fat mass, however, the size of individual fat cells, and the act of overeating, it is interesting that it is not affected by exercise for comparison, IL-6 is released in response to muscular contractions. Thus, it is speculated that leptin responds specifically to adipose-derived inflammation. Taken as such, increases in leptin levels in response to caloric intake function as an acute pro-inflammatory response mechanism to prevent excessive cellular stress induced by overeating.
When high caloric intake overtaxes the ability of fat cells to grow larger or increase in number in step with caloric intake, the ensuing stress response leads to inflammation at the cellular level and ectopic fat storage, i. The insulin increase in response to the caloric load provokes a dose-dependent rise in leptin, an effect potentiated by high cortisol levels.
This response may then protect against the harmful process of ectopic fat storage, which perhaps explains the connection between chronically elevated leptin levels and ectopic fat storage in obese individuals.
Although leptin reduces appetite as a circulating signal, obese individuals generally exhibit a higher circulating concentration of leptin than normal weight individuals due to their higher percentage body fat. A number of explanations have been proposed to explain this. An important contributor to leptin resistance is changes to leptin receptor signalling, particularly in the arcuate nucleus , however, deficiency of, or major changes to, the leptin receptor itself are not thought to be a major cause.
Other explanations suggested include changes to the way leptin crosses the blood brain barrier BBB or alterations occurring during development. Studies on leptin cerebrospinal fluid CSF levels provide evidence for the reduction in leptin crossing the BBB and reaching obesity-relevant targets, such as the hypothalamus, in obese people.
Since the amount and quality of leptin receptors in the hypothalamus appears to be normal in the majority of obese humans as judged from leptin-mRNA studies ,  it is likely that the leptin resistance in these individuals is due to a post leptin-receptor deficit, similar to the post-insulin receptor defect seen in type 2 diabetes.
When leptin binds with the leptin receptor, it activates a number of pathways. Mice with a mutation in the leptin receptor gene that prevents the activation of STAT3 are obese and exhibit hyperphagia. The PI3K pathway may also be involved in leptin resistance, as has been demonstrated in mice by artificial blocking of PI3K signalling.
The PI3K pathway also is activated by the insulin receptor and is therefore an important area where leptin and insulin act together as part of energy homeostasis. The consumption of a high fructose diet from birth has been associated with a reduction in leptin levels and reduced expression of leptin receptor mRNA in rats. Long-term consumption of fructose in rats has been shown to increase levels of triglycerides and trigger leptin and insulin resistance,   however, another study found that leptin resistance only developed in the presence of both high fructose and high fat levels in the diet.
A third study found that high fructose levels reversed leptin resistance in rats given a high fat diet. The contradictory results mean that it is uncertain whether leptin resistance is caused by high levels of carbohydrates or fats, or if an increase of both, is needed. Leptin is known to interact with amylin , a hormone involved in gastric emptying and creating a feeling of fullness. When both leptin and amylin were given to obese, leptin-resistant rats, sustained weight loss was seen.
Due to its apparent ability to reverse leptin resistance, amylin has been suggested as possible therapy for obesity. It has been suggested that the main role of leptin is to act as a starvation signal when levels are low, to help maintain fat stores for survival during times of starvation, rather than a satiety signal to prevent overeating. Leptin levels signal when an animal has enough stored energy to spend it in pursuits besides acquiring food.
Dieters who lose weight, particularly those with an overabundance of fat cells, experience a drop in levels of circulating leptin. This drop causes reversible decreases in thyroid activity, sympathetic tone, and energy expenditure in skeletal muscle, and increases in muscle efficiency and parasympathetic tone. A decline in levels of circulating leptin also changes brain activity in areas involved in the regulatory, emotional, and cognitive control of appetite that are reversed by administration of leptin.
Osteoarthritis and obesity are closely linked. Obesity is one of the most important preventable factors for the development of osteoarthritis.
Originally, the relationship between osteoarthritis and obesity was considered to be exclusively biomechanically based, according to which the excess weight caused the joint to become worn down more quickly. However, today we recognise that there is also a metabolic component which explains why obesity is a risk factor for osteoarthritis, not only for weight-bearing joints for example, the knees , but also for joints that do not bear weight for example, the hands.
Thus, the deregulated production of adipokines and inflammatory mediators, hyperlipidaemia, and the increase of systemic oxidative stress are conditions frequently associated with obesity which can favour joint degeneration. Furthermore, many regulation factors have been implicated in the development, maintenance and function, both of adipose tissues, as well as of the cartilage and other joint tissues.
Alterations in these factors can be the additional link between obesity and osteoarthritis. Adipocytes interact with other cells through producing and secreting a variety of signalling molecules, including the cell signalling proteins known as adipokines. Certain adipokines can be considered as hormones, as they regulate the functions of organs at a distance, and several of them have been specifically involved in the physiopathology of joint diseases. In particular, there is one, leptin, which has been the focus of attention for research in recent years.
The circulating leptin levels are positively correlated with the Body Mass Index BMI , more specifically with fatty mass, and obese individuals have higher leptin levels in their blood circulation, compared with non-obese individuals.
In addition to the function of regulating energy homeostasis, leptin carries out a role in other physiological functions such as neuroendocrine communication, reproduction, angiogenesis and bone formation.
More recently, leptin has been recognised as a cytokine factor as well as with pleiotropic actions also in the immune response and inflammation. Leptin has thus emerged as a candidate to link obesity and osteoarthritis and serves as an apparent objective as a nutritional treatment for osteoarthritis.
As in the plasma, the leptin levels in the synovial fluid are positively correlated with BMI. Leptin has been shown to be produced by chondrocytes, as well as by other tissues in the joints, including the synovial tissue, osteophytes, the meniscus and bone.
The risk of suffering osteoarthritis can be decreased with weight loss. This reduction of risk is related in part with the decrease of the load on the joint, but also in the decrease of fatty mass, the central adipose tissue and the low-level inflammation associated with obesity and systemic factors.
This growing evidence points to leptin as a cartilage degradation factor in the pathogenesis of osteoarthritis, and as a potential biomarker in the progression of the disease, which suggests that leptin, as well as regulation and signalling mechanisms, can be a new and promising target in the treatment of osteoarthritis, especially in obese patients.
Obese individuals are predisposed to developing osteoarthritis, not only due to the excess mechanical load, but also due to the excess expression of soluble factors, that is, leptin and pro-inflammatory cytokines, which contribute to joint inflammation and cartilage destruction.
As such, obese individuals are in an altered state, due to a metabolic insufficiency, which requires specific nutritional treatment capable of normalising the leptin production and reducing the systematic low-level inflammation, in order to reduce the harmful impact of these systematic mediators on the joint health.
There are nutritional supplements and pharmacological agents capable of directing these factors and improving both conditions. Leptin was approved in the United States in for use in congenital leptin deficiency and generalized lipodystrophy.