A fitness boot camp is a type of group physical training program conducted by gyms, personal trainers, and former military personnel. These programs are designed to build strength and fitness through a variety of intense group intervals over a 1 hour period of time. Originally popular in the US, they were brought over to the UK in 1999 and have been growing in popularity ever since. Boot Camp training often commences with dynamic stretching and running, followed by a wide variety of interval training, including lifting weights/objects, pulling rubber TRX straps, pushups/situps, plyometrics, and various types of intense explosive routines. Sessions usually finish with yoga stretching. Many other exercises using weights and/or body weight, similar to CrossFit routines, are used to lose body fat, increase cardiovascular efficiency, increase strength, and help people get into a routine of regular exercise. Many programs offer nutrition advice as well. It is called "boot camp" because it trains groups of people, may be outdoors, and may or may not be similar to military basic training. The term "boot camp" is currently used in the fitness industry to describe group fitness classes that promote fat loss, camaraderie, and team effort. They are designed to push people a little bit further than they would normally push themselves in the gym alone. Boot Camps are sometimes organized outdoors in parks using bodyweight exercises like push ups, squats, suspension training and burpees, interspersed with running and competitive games. The idea is that everyone involved works at their own pace as they team up and work towards one goal, either in pairs, small teams of three or four, or even two teams head on. Boot camps provide social support for those taking part. This provides a different environment for those exercisers who get bored in a gym and so find it hard to develop a habit of exercise. Participants make friends and socialize as they exercise, although how strict the trainers or drill instructors in charge can be will depend on the company running the camp. Members of fitness boot camps are usually tested for fitness on the first day and then retested at the end of the camp, which usually runs for between 4 and 6 weeks. Fitness boot camps are often based on the military style of training, although that has started changing over the last few years. An advantage of a boot camp is that the large group dynamic will often help motivate the participants. A growing trend in fitness boot camps are the indoor locations which prove to be climate proof and provide a better workout environment for the members. Additionally, some camps include extracurricular fitness activities off-site. There are many other benefits of a fitness boot camp, which includes mental health. It has long been known[by whom?] that regular aerobic exercise can help to reduce high blood pressure, hypertension and combat stress. Part of this is due to the release of endorphins, which act as a mood elevator. Some "Holistic Bootcamps"[which?] provide the mental coaching required to sustain motivation after people leave the camp. Themed fitness bootcamps often consist of the use of one particular training implement to the exclusion of others. Kettlebells are the preferred tool for kettlebell fitness bootcamps run by RKC instructors and TRX suspension trainers are the preferred tools for TRX instructors. Boxing themed fitness bootcamps often use heavy bags. The use of themes vary widely between fitness bootcamps and their instructors according to the preferences between the instructor and the needs and likes of the clientele.