Help you choose: OpenSim, BoB, AnyBody, which biomechanics analysis software is better to use and more suitable?

Just getting into biomechanical analysis, how should one choose among various biomechanical analysis software? Only those who have truly used various biomechanical analysis software can give us some advice!

Recently, I saw an evaluation of biomechanical analysis software used by three scholars from Chalmers University of Technology - Sports Technology Center online. This article was originally published at the 11th International Sports Engineering Association conference in 2016. Personally, I feel that the evaluation of biomechanical analysis software in the article is very objective and worth our reference.

The biomechanical analysis at Chalmers University of Technology - Sports Technology Center is focused on swimming, using OpenSim,BoB, AnyBody, and SWUM software. Since the SWUM software does not have an interface with the motion capture system to import motion data, we will not consider it for now. The experts at Chalmers University of Technology - Sports Technology Center provided the following descriptions regarding the use of OpenSim,BoB, and AnyBody:

When the motion capture system has .trc format, kinematics from the motion capture system can be imported. When force plate measurements, center of pressure data, or joint angles have .sto or .mot format, they can be added to the OpenSim analysis. EMG can only be imported for comparison with the simulation (.sto or .mot files).

Biomechanical data can be analyzed through the following specific steps: First, scale the predefined musculoskeletal model to the static marker data recorded for the object of interest (Figure 1a). The scaling process fits many variables, such as bone and muscle lengths, the center of mass position for each bone, and the mass of each segment (including bones and muscles) to the recorded subject. Then, inverse kinematics or inverse dynamics analysis can be performed to calculate joint moments from joint angles and external forces (Figure 1b). Residual reduction analysis (RRA) minimizes the mismatch between the recorded trajectory and the recorded ground reaction forces. Static optimization can then be performed to further decompose the computed net joint moments into individual muscle forces at each time point. The entire analysis can then be transformed into a simulation of the complete movement, including muscle activation of the relevant muscles.

The inverse dynamics calculator requires four input files (motion, force, skeletal properties, muscle properties), and the user defines the duration and time increment of the simulation.

To define the motion of the model, motion files (.txt, .csv, .c3d) must be added. Each file format requires certain naming conventions for anatomical markers and a specific number of anatomical markers; for example, a c3d file requires 30 markers arranged (Vicon naming). BoB will run in the absence of markers, but if necessary markers to define segments on both sides of a joint cannot be found, the joint will not be able to hinge. If markers are missing from the investigation, users can create virtual markers by offsetting real markers (e.g., the left front head is 100mm to the left of the right front head) [20].

External forces or ground reaction forces must be known and manually inserted into the .txt file (amplitude, speed/frequency, time, application point). If the user does not know the forces, the program can approximate them to some extent.

The skeletal model (.txt file) can be adjusted based on the height/weight of the object generating the motion file.

Possible misalignments of limbs/bones can also be modeled.

Information about all considered muscles is stored in a .mat file, which can be accessed through the BoB interface, and different muscles can be added/edited/excluded. Inserting new muscles requires a comprehensive understanding of their geometry, insertion points, forces, fiber lengths, etc.

After inserting the four input files, BoB will calculate the posture of the model and solve the inverse dynamics problem to determine the loads within the muscles, joints, and bones. Once the inverse dynamics solver is complete, the "play" button will animate the motion and allow observation of different muscle activations. The results can be displayed in movies, images, tables, or graphs using the output dropdown menu.

AnyBody is currently the most complex and feature-rich muscle and skeletal modeling software tool available, but it must be purchased to use.

It treats the musculoskeletal system as a rigid body system, thus allowing the application of standard computational methods of multibody dynamics. The default human model can be easily adapted to the user's needs (height, weight, segment lengths, strength, skeletal geometry). Additionally, objects, loads, and motion conditions can supplement the conditions of the task being discussed (Figure 3). If a full-body model is used, 458 muscles need to be considered [21,22].

The environment in the simulation can be modeled (STL format can be imported), for example, adding a bicycle or exercise machine to the modeling setup. Electromyographic signals can only be used as a validation tool and cannot be used as input to drive the model.

There are interfaces with other software (such as SolidWorks, Ansys, Abaqus, etc.) that open up new possibilities. The model itself can be driven by the following inputs:

• Motion input can be provided from .c3d or .bvh files. It is valuable to use at least three markers for each body segment. The model requires input from a three-dimensional motion tracking system.

• Force input

• Environmental input (connecting the skeleton to a moving surface)

• GUI synthesized motion (manually moving bones)

Modeling is done in the AnyScript language, which is a declarative object-oriented language. Each model is divided into two main parts: the model part (mechanical systems, motion, environment) and the research part (operations such as motion or dynamics analysis). AnyBody uses inverse dynamics methods to solve the redundancy problem of muscle recruitment by referencing the central nervous system (CNS). All muscle and joint forces can be determined as a solution to an optimization problem that represents the CNS's desire to minimize the load on the muscles. AnyBody provides seven different scaling methods, with the most advanced method also considering body fat percentage. Possible methods of using this software include changing simple parameters (such as load, posture) to calculate muscle responses during the task, or adjusting one of the existing musculoskeletal motion capture models to new laboratory settings, force platforms, and the availability of laboratory coordinate systems by redefining the marker protocol, or completely designing a human model and its environment from scratch. This can be beneficial when analyzing animals or unstudied joints or postures.

I read the entire article, and it can be preliminarily understood that the viewpoint of Chalmers University of Technology - Motion Technology Center is: for users doing academic projects, choosing OpenSim is more appropriate, as it is free, has a large number of users, and a large community sharing usage experiences, developed codes, extended model templates, and papers, which can provide more support for academic work; for users doing motion analysis and biomechanics teaching, choosing BOB is more suitable because it has a simple interface, is easy to operate, has many built-in models, and allows for an intuitive understanding of joint contact forces, joint torques, motion trajectories, and muscle activation; for users focusing on the interaction between humans and the environment or surgical planning, the more expensive AnyBody is more suitable, although it requires learning the use of AnyScript language, which is very complex, but it is more powerful and can be adjusted in detail according to user needs.

Every tool has its own advantages and disadvantages. As users, the most critical thing is to know what we want to do and then make the right choice. BOB is a product with good cost performance, although it is not free like OpenSim, and currently, there is not much information introducing its usage experience or sharing works, but it is easy to get started, has a short learning curve, can easily import external data, and BOB includes a model composed of over 600 muscle units, while OpenSim, as far as I know, has only about 140.

As mentioned at the beginning of this article, if you haven't used it and only heard others describe it, it always feels a bit unreliable. AnyBody is somewhat expensive, and we can have the opportunity to try it again, but for BOB and OpenSim, we can completely try it ourselves! BOB supports free trials, and OpenSim is free, so let's take action together! Who knows, we might soon be the ones sharing experiences!

BOB can be applied for a free trial via email.Please send the following information to info@deanwell.com.cn:

OpenSim can be downloaded directly from their official website: https://simtk.org/projects/opensim

However, downloading requiresregistering a SimTK account. If it is inconvenient to register, you can go tohttps://github.com/opensim-org/opensim-gui/releasesto download!