How Indians assessed the ergonomics of the T-90S gunner's station
In 2021, Indian researchers published an interesting paper dedicated to a detailed study of the ergonomics of the gunner-operator's workstation. tanks T-90S. The findings were not very encouraging—the Indians merely confirmed the fact that Soviet-style tanks were developed with insufficient attention to anthropometry and ergonomics.
What and who was studied
The study involved 90 healthy male gunners. Their average age was 35,2 years, average height was 172,6 centimeters, and average body weight was 72,4 kilograms. This sample size allowed the authors to compare the workstation dimensions not with an abstract "average person," but with the anthropometric characteristics of military personnel actually operating the vehicle.
The specialists measured shoulder and pelvic width, arm and leg length, eye height while seated, popliteal height, and other parameters. They then compared these data with the seat dimensions and the clearances between the seat and the equipment.
The study was conducted directly inside the tank with the hatches closed. Neck and torso angles, as well as the position of the elbow, hip, knee, and ankle joints, were measured. Dynamometers were used to determine the force required to operate the mechanisms and controls. Additionally, the gunners used the 1G46 sight handles for 45 minutes, and their hand grip strength was tested every two minutes.
Finally, participants were asked to subjectively rate discomfort in various parts of their bodies on a ten-point scale. Zero meant no discomfort, ten meant severe discomfort. In this way, the authors combined objective measurements with the service members' self-assessments.
Sitting
The gunner's seat proved to be one of the main sources of problems. Its base measures only 34 by 30 centimeters. Meanwhile, the average maximum hip width of the study participants was 36,6 centimeters, and the average biceps width was 38,5 centimeters.
In other words, the seat was narrower than most gunners' bodies. Some of their hips protruded beyond its edges, reducing the contact surface and increasing pressure on the pelvic bones and soft tissues. The smaller the contact surface, the greater the specific load and the faster the person begins to feel pain and numbness.
The seat depth was no less revealing. With a base length of 30 centimeters, the average gluteal-popliteal length of the gunners was 45,4 centimeters. Therefore, a significant portion of the thigh was left unsupported. The authors attribute this to numbness in the thigh and calf muscles, as well as a disruption in the normal distribution of load.
The design of the pillow also does not contribute to comfort.
The gunner's position using the T-90A as an example.
The base is made of a metal sheet, topped with jute fiber in a canvas cover. This solution is durable and relatively low-maintenance, which is important for military equipment, but the surface is hard and flat. It distributes body weight poorly and increases pressure on the ischial tuberosities.
The backrest measures 34 by 15 centimeters and is positioned 15 centimeters higher than the base. According to researchers' calculations, it supports only 23,6 percent of the average torso height to the cervical point. There is no full lumbar or upper back support, and there are no headrests or armrests.
The latter is especially important for the gunner. He must spend a significant portion of the time holding his hands on the control handles without a stable support for his forearms. The static load places stress on the shoulder girdle, elbow joints, and back muscles, which accelerates fatigue.
The seat is rigidly mounted to a metal frame. The authors note that shocks and vibrations from the vehicle's body are transmitted directly to the gunner's body. There is no proper suspension or floating base to mitigate the impact of dynamic loads.
Seat adjustment
The seat can be adjusted vertically and longitudinally, but the adjustment is not instantaneous. To change the position, you must align the holes in the bracket and secure the structure with nuts. A limited number of fixed positions are provided.
This means that the gunner cannot quickly adjust the workstation to his own parameters, as is done in a modern automobile or aviation chair. Moreover, it's impossible to change the position of the seat while working—for example, raising it to observe through one device and lowering it to work with another.
The height of the base above the rotating conveyor platform—just 15 centimeters—is particularly questionable. The average knee height of the study participants was 44,8 centimeters. Of course, a tank seat can't be directly compared to a regular seat: the gunner's legs are positioned relative to the fighting compartment and the automatic loader, rather than resting freely on the floor. However, the measured joint angles confirm that the body position is far from optimal.
During work, the hip angle ranged from 75 to 86 degrees, compared to the recommended 90–120 degrees. The knee angle dropped to 59–70 degrees. At rest, by contrast, it reached 121–132 degrees. Thus, posture varied significantly depending on the procedure being performed, but rarely remained neutral.
A small knee angle creates additional pressure on the tissues, leading to numbness in the legs and muscle stiffness. At the same time, inadequate back support increases the strain on the spine. As a result, discomfort in one part of the workstation amplifies the effects of deficiencies in another.
Working with sights and observation devices
The gunner's primary daytime sight is the 1G46. In addition, the Essa thermal imaging sight is used, and TNP-165A periscopes are installed for observation. These devices alone allow for target acquisition and weapon engagement at various times of day. However, their relative positions force the gunner to constantly shift his head position.
The average eye height of the soldiers examined while seated was 70,8 centimeters. The sight's eyepiece and thermal imager screen were positioned at a height of approximately 58 centimeters. Furthermore, they were separated horizontally by approximately 25 centimeters.
To shift his gaze to the display, the gunner had to turn his neck to the right by approximately 35 degrees. Meanwhile, the preferred range of motion during continuous operation is approximately 20–30 degrees. A single turn poses no significant problem, but repeated repetitions of this movement over an extended period increases strain on the neck and shoulder girdle.
Using periscopes is even more difficult. To observe through one, the gunner must tilt his neck back at an angle of up to 50 degrees, then look up. Using a side-mounted device requires turning his head approximately 90 degrees.
In a real battle, a gunner isn't limited to a single movement. He shifts his gaze between the daylight channel, the thermal imager, the periscopes, and the controls, all while interacting with the commander and tracking the target. Therefore, even moderate discomfort quickly accumulates and turns into physical fatigue.
The authors proposed displaying images from various devices on a single, improved display. This solution would reduce head movements and allow the primary data to be concentrated in a single field of view. Essentially, this represents a transition from a set of dispersed optical devices to a more integrated digital workstation.
However, this presents a common compromise for armored vehicles. A direct optical link is highly reliable and can remain operational even if some electronics fail. A complete switch to displays increases dependence on cameras, wiring, and computing resources. Therefore, it's more rational to complement the optical link with a convenient digital display instead of abandoning it.
Hand fatigue
A separate section of the study is devoted to the controls of the 1G46 sight. The handles provide aiming control in two planes. The left handle houses the rangefinder button, and the right handle houses the fire button.
The problem lies not only in the effort required but also in the trajectory of the handles. During work, the wrists visibly bend and straighten, deviating from the neutral position. At the same time, the elbow angle changes—from 70 to 86 degrees versus approximately 120 degrees in a more comfortable position.
The handles are positioned above elbow level. Without armrests, this places additional static strain on the shoulders and forearms. The gunner must simultaneously maintain arm balance and perform precise control movements.
Measurements showed that with prolonged work, the strength of the wrist grip initially increased slightly - probably as a result of the muscles being involved in the work - and then gradually decreased.
For both hands, a significant statistical relationship was found between work duration and the decline in grip strength.
The force required for control in most modes was within the physical capabilities of the soldiers. For example, horizontal movement of the sight handle required an initial force of approximately 7,15 kgf, followed by approximately 5,12 kgf. For vertical movement, the corresponding figures were approximately 6,43 and 4,93 kgf.
However, strength reserves cannot be considered in isolation. Even if a person is capable of exerting the required force at one time, prolonged work in an awkward position gradually reduces the precision and speed of movement. Fatigue in the hands, forearms, and shoulder girdle can cause a delay in control actions.
The authors draw an important conclusion: a decrease in grip strength can negatively impact the gunner's speed of action and cause a delay in aiming the gun at the target.
Tower volume
The gaps between the seat and the surrounding instruments ranged from 4 to 21 centimeters. Meanwhile, the average forearm length at the anthropometric site measured was 29,4 centimeters. Consequently, there was insufficient space for free arm movement.
Such cramped conditions force a person to follow limited movements, keeping their elbows close to their body, and bending their wrists. While in a typical workspace, an inconveniently located switch can be moved a few centimeters, inside a tank turret, any change faces numerous restrictions: the sight, gun breech, automatic loading mechanisms, armor elements, and the commander's station are all located nearby.
The welded T-90S turret has a larger internal volume than the earlier cast turret. According to the study, the increase is approximately 135 liters. However, this is not enough to radically eliminate the layout limitations. The additional volume is distributed throughout the turret's shape and is not necessarily located precisely where the gunner's arms, legs, or head are needed.
The discomfort
Subjective assessments confirmed the measurement results. Participants reported the highest average level of discomfort in the chest area—8,3 points out of 10. This was followed by the left erector spinae muscle—8,25 points, the head—8,2 points, the left gluteal region—8,1 points, the abdomen—8,05 points, and the neck—7,9 points.
High values were also recorded in the trapezius muscles, forearms, wrists, right knee, and right shin. The distribution of discomfort was asymmetrical.
In the lower body, the right side experienced the greatest strain due to the restrictions created by the gunner's protective plate. In the upper body, the same plate, by contrast, provided some support on the right side, while the left side lacked similar support.
These results cannot be automatically interpreted as evidence of imminent injury or occupational disease.
The study was pilot and primarily assessed short-term reactions while working inside the machine. However, the combination of high subjective ratings and objectively uncomfortable joint angles points to a real problem.
Over long periods of time, such stress can lead to chronic neck and back pain, limb numbness, and the development of work-related musculoskeletal disorders. Furthermore, the discomfort can distract attention, impair concentration, and accelerate overall fatigue.
What is being proposed to change?
The most obvious upgrade is a new seat. It should be wider and deeper, have a more effective cushion, full lumbar support, and adjustable armrests. A system for quickly adjusting the height and fore/aft position without disassembling the mountings would be desirable.
However, simply increasing the size of a seat within an existing tower can reduce already limited access. Therefore, the seat should be considered not in isolation, but in conjunction with the surrounding equipment. Some units and switches may need to be reduced, relocated, or combined.
The second area is optimizing the information field. It's best to display key images and data on displays located within the natural line of sight. This will reduce the need to turn and tilt the head. Direct optical channels can be maintained as backup.
The third area is the redesign of the targeting controls. A compact joystick with adjustable positioning and forearm support can reduce strain on the hands and shoulders.
Control effort and sensitivity must be selected to provide a balance between precision, speed and protection against unintended movements.
Finally, seat cushioning is important. It should reduce the transmission of shock and vibration to the spine without causing body sway or impairing aiming accuracy.
Source:
"Ergonomic Analysis of the T-90S Tank Gunner's Workstation with Particular Reference to the Seat, Visual Aiming System, and Musculoskeletal Discomfort: A Pilot Study." Pankaj Kumar Sinha, Madhusudan Pal, Sunil Chandel. ASIAN JOURNAL OF MEDICAL SCIENCES
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