Mostly what I've found is anecdotal. Would love to know if there has been any actual research on this subject. I've tried both and don't find a dramatic difference, wondering if investing in a geekdesk or equivalent is worth it.
Here is some information from UCLA
No one will stand all day when they have the opportunity to sit. This is because the body works harder when standing than when sitting. However, work production studies indicate that workers are more efficient when they stand to work.
Jobs that are most appropriately done standing include construction workers, highway flaggers, medical personnel, painters, electricians, plumbers, loggers, firefighters, plant inspectors, and maintenance personnel.
Sitting is better when visually intensive or precise work is required, the activity is of a repetitive nature; longer tasks are completed (greater than 5 minutes), and when everything can be placed within easy reach. Sitting is not appropriate when heavy objects must be handled or long reaches are required.
However, prolonged sitting has been associated with a high incidence of back complaints (Mandal, 1981), increased spinal muscular activity and intradiscal pressure (Grandjean and Hunting, 1977; Lindh, 1989). Other problems reported include discomfort in the lower extremities (Westgaard and Winkel, 1996) and increased muscle loading of the neck and shoulder muscles when sitting with the forearms unsupported as compared to standing with the forearms unsupported (Aaras et al., 1997; Lannersten and Harms-Ringdahl, 1990).
To summarize the literature, neither static standing nor sitting is recommended. Each position has its advantages and disadvantages.
Research indicates that constrained sitting or constrained standing are risk factors and that alternating work postures may be preferable. Roelof and Straker (2003) recorded the discomfort and preferences of 30 bank tellers who worked in just sitting, just standing and alternating sitting and standing work postures. Greatest discomfort in the upper limb was noted in the just sitting posture and greatest discomfort in the lower limb and back was reported for the just standing posture. Alternating between sitting and standing resulted in least discomfort and was reported as the preferred posture by 70% of subjects.
Visser and Straker (1994) studied dental hygienists and determined that breaking up constrained work postures increased postural changes that reduced musculoskeletal discomfort and fatigue in most body areas. Graf et al. (1995) associated work tasks with less frequent postural change as being associated with a higher prevalence of MSD. Hagberg and Sundelin (1986) reported that frequent rest intervals can assist in reducing the perception of postural discomfort. All these studies support the role of postural variation and breaks in reducing or delaying musculoskeletal discomfort.
Workstations which allowed both sitting and standing were introduced to postal workers by Nerhood and Thompson (1994), with a subsequent reduction in discomfort reported. Similarly, Paul (1995a; 1995b) reported decreased foot swelling and increased perceived energy and less tiredness in a group of VDU workers given sit/stand workstations. These workers were encouraged to stand for 15 minutes every hour. Hedge and Ray (2004) reported decreased discomfort levels and increased self-perceived productivity in a study of Intel workers using electric height-adjustable tables.
An alternating sit/stand work posture reduces the amount of workload experienced by body parts throughout the day. Greatest reduction of discomfort occurs as the workday progresses. Alternation between two postures allows for increased rest intervals of specific body parts, and reduced potential for risk factors commonly associated with MSD development.
Ideally, provide workers with a workstation and job tasks that allow frequent changes of working posture, including sitting, standing, and walking. If either sitting or standing is feasible but only one possible, sitting in a properly designed chair is preferable. (Unsupported sitting, for example, results in disk pressures 40 percent greater than during standing work (cited by Yates & Karwowski, 1992) Minimizing Risks when Standing
However, in many situations, sitting is just not a feasible option and workers must stand. Here are some workstation and workplace design features that can help minimize the risk factors associated with standing work.
Workers who stand are somewhat unstable. A standing person is like a tall building swaying in the wind. According to research cited by Whistance, Adams, van Geems & Bridger (1995), individuals required to stand for prolonged periods adopt asymmetrical standing attitudes four times more often than symmetrical attitudes. Shifting the weight from foot to foot provides an important relief mechanism. People tend to stand with one foot forward, which increases their stability and can reduce twisting stress if the person turns to the side opposite of the forward foot.
The body of standing person also rocks forward and backward and from side to side. The anterior-posterior sway is greater than the lateral sway. Compensatory muscle activity is required to counterbalance the continuously moving gravitational moments acting around the joints.
Use a footrest at standing workstations to help compensate for postural sway. The use of a footrest reduces intravertebral disc stress by preventing excessive lordosis (Whistance, Adams, van Geems & Bridger, 1995). In a study cited by Rys and Konz (1994), subjects were allowed to stand with no footrest or stand and use one of three different footrests: a flat platform, 15-degree angled platform, or a 50 mm bar. They used the footrest options significantly more than standing without a footrest. They used the bar significantly less than the other two footrest options. The bar was used 59 percent of the time, and the other two platforms were used approximately 80 percent of the time. Subjects switched their foot from the floor to one of the footrests once every 90 seconds.
Floor mats can also be helpful when standing. Floor mats encourage the body to naturally and imperceptibly sway, encouraging subtle movement of the calves and leg muscles (King, 2002). Research supports that various floor mats are preferred over concrete floors for standing work. In one of the more recent articles, Cham and Redfern (2001) reported that "floor mats characterized by increased elasticity, decreased energy absorption, and increased stiffness resulted in less discomfort and fatigue". Interestingly, they found that differences in reported musculoskeletal discomfort could not be significantly detected until the third hour of testing.
A field study investigated floor mats and shoe insoles for reducing standing fatigue (King, 2002). Four conditions were studied, each including a hard wood-block floor as the base: a) standing on a hard wood-block floor, b) standing on a floor mat, c) wearing shoes with insoles, and d) standing on a floor mat wearing shoes with insoles. Subjects were exposed to each condition for one work week (40 hours). Fatigue and discomfort were measured using questionnaires. In general, the mat, insoles, and combined condition of insoles and mat were more comfortable than standing on the hard wood-block floor. However, there was no significant difference between the conditions of using insoles or using both insoles and a mat. More research is encouraged in this area using more reliable and sensitive measures.
What about shoes? Konz & Johnson (2000) offer the following advice: Use shoes that mold to your feet and cause a minimum of pressure on all parts of your foot. Because of the swelling during standing, purchase shoes one-half to one size larger than you normally would. A good time to buy work shoes is right after you have been standing for an extensive length of time. Most of the swelling takes place in the midfoot, lowering the arches and increasing the width of the foot (Rys & Konz, 1994). Buy shoes that allow you to wiggle your toes. People who stand for long hours should buy shoes that have laces at the ball and the top of the foot, to allow for swelling and also to make adjustments for two different-sized feet. There can be a 5-10 percent difference in the size of a person's feet (Rys & Konz, 1994).
Workstations used in a standing position require sufficient foot clearance. When there is insufficient foot clearance, the worker must stand farther away from the workspace and tends to lean forward in an unhealthy, awkward posture. Recommended foot clearance space is 4”.
I don't think there are any studies relating directly to productivity. However, there are strong, long-known and well-documented health benefits connected to frequently varying your working position. Sitting for long periods of time has been shown to increase the risk of health problems, including heart diseases and diabetes.
There is no research on how often you should switch position. But as a rule of thumb, it is safe to say that you should do that at least once every hour. Having a program to remind you is a smart thing. Of course, interruptions can disturb your "flow" and hurt your productivity. But, since an unhealthy person is unlikely to be productive, I'd say the strong health benefits of varying your position is good for your productivity in the long run.
Investing in a "geekdesk" or similar should be regarded as a long-term health investment (you are unlikely to note any short-term benefits), and as such it is very wise.