Ballistic movement can be defined as
muscle
Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...
contractions that exhibit maximum velocities and accelerations over a very short period of time. They exhibit high firing rates, high force production, and very brief contraction times.
Physiology
Muscle contraction
The
muscle contraction
Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such as ...
of a ballistic muscle movement can exhibit a
muscle coactivation
Muscle coactivation occurs when agonist and antagonist muscles (or synergist muscles) surrounding a joint contract simultaneously to provide joint stability. It is also known as muscle cocontraction, since two muscle groups are contracting at t ...
of concurrent agonist and antagonist muscles or the characteristic triphasic agonist/antagonist/agonist muscle activation.
Electromyography
Electromyography (EMG) is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG is performed using an instrument called an electromyograph to produce a record called an electromyogram. An electromyog ...
(EMG) recordings of demonstrate the triphasic muscle activation begins with a brief agonist motor unit activation signal with firing rates of 60 to 120 Hz that may last for 100ms and occurs 50 to 100ms before movement begins. The firing rates of ballistic movements are much higher than that of slow ramp movements (5–15 Hz). The brief agonist muscle contraction is thus followed by antagonist muscle unit activation. The degree of antagonist muscle unit activation is dependent on the task at hand unlike the first agonist muscle activation which is independent to environmental stimuli. The function of the antagonist muscle contraction is believed to control the amplitude and timing of ballistic movements. Antagonist muscle contraction may serve to prevent injury to joints by preventing the limb from overextending itself and also function to control the distance and time the limb is being moved. Experiments involving ballistic movement of small amplitudes show a marked increase in antagonist muscle activation and experiments where distance moved is not controlled antagonist muscle activation was decreased or absent. The second agonist muscle activation is suggested to terminate the negative acceleration of the antagonist muscle contraction and thus the ballistic movement.
Power and energetics
Elastic storage of energy
Ballistic movements are often powered through
elastic energy
Elastic energy is the mechanical potential energy stored in the configuration of a material or physical system as it is subjected to elastic deformation by work performed upon it. Elastic energy occurs when objects are impermanently compressed, ...
storage and subsequent recovery mechanisms. The
power
Power most often refers to:
* Power (physics), meaning "rate of doing work"
** Engine power, the power put out by an engine
** Electric power
* Power (social and political), the ability to influence people or events
** Abusive power
Power may a ...
required to produce the extremely rapid velocities of ballistic movements is made possible through muscle work being stored in elastic elements (such as
tendons
A tendon or sinew is a tough, high-tensile-strength band of dense fibrous connective tissue that connects muscle to bone. It is able to transmit the mechanical forces of muscle contraction to the skeletal system without sacrificing its ability ...
,
aponeuroses
An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join muscl ...
, or even muscle). Muscle work is applied to these elastic elements over a relatively slow period of time, and is released very rapidly. Higher power output is produced because the energy is released in a much shorter amount of time than it is stored. In this sense the power of the muscles is actually amplified. When energy is produced by muscle contraction, stored in a tendon, then released to increase mechanical energy of the body (or body segment), muscle power is amplified. It is important to note, however, that the term power ‘amplification’ may be deceptive. In animals, elastic mechanisms never add energy to the system; they amplify power in the sense that the energy is released more rapidly than it is stored.
Possible benefits
Ballistic systems are capable of power outputs that are significantly greater than that of the muscles associated with the actual movement. One prime example of this is tongue projection in
salamanders
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
. This decoupling of muscle work from body/limb work is a major benefit of elastic energy storage mechanisms. Another benefit resulting from this decoupling is decreased thermal dependence of ballistic movement. Deban and Lappin analyzed the prey capture behavior of
toads
Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands.
A distinction between frogs and toads is not made in scienti ...
(Bufo terrestris), which involves two types of movement: elastically powered, ballistic movement (mouth opening and tongue projection) and muscle-powered movement (tongue retraction and mouth closing). The toad feeding was observed across a range of temperatures (11–35 °C), and the kinematic, dynamic, and electromyographic variables were measured and analyzed. Over the 11–35 °C temperature range, the ballistic movements had
Q10 values very close to 1 (Q
10 = 0.99–1.25), signifying thermal independence and supporting the main hypothesis. The muscle-powered movements had a higher temperature coefficient (Q
10 = 1.77–2.26), signifying thermal dependence.
Another example of a thermally independent ballistic movement is tongue projection in
chameleons
Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...
. It was discovered that veiled chameleons (Chamaeleo calyptratus) were able to perform this high-performance tongue projection, and successful prey capture, across a wide range of temperatures (15 °C–35 °C). Anderson and Deban also found a contrast between thermal dependence of tongue projection and retraction (which is not elastically-powered). This further supports the hypothesis that the elastic recoil mechanism is responsible for the decreased thermal dependence of ballistic tongue projection.
Examples
Trap-jaw ants
In trap-jaw ants (
Odontomachus
''Odontomachus'' is a genus of ants commonly called trap-jaw ants found in the tropics and subtropics throughout the world.
Overview
Commonly known as trap-jaw ants, species in ''Odontomachus'' have a pair of large, straight mandibles capabl ...
bauri) ballistic movement can be seen in their extremely rapid mandible strikes. The trap-jaw ants mandible has an average closing speed of 38.4 m/s and can produce forces that are 371-504 times the weight of the ant. The ants use these extremely powerful mandible strikes in several novel ways. When the ant attacks a larger animal it will strike the animal and at the same time use the force from the strike to propel itself away from the animal. When facing prey of similar size such as another ant the strike actually results in both animals being propelled away from each other. When the ant is trying to flee from a predator it will strike at the substrate and propel itself vertically into the air.
Crickets
In crickets (
Acheta domesticus
''Acheta domesticus'', commonly called the house cricket, is a cricket most likely native to Southwestern Asia, but between 1950 and 2000 it became the standard feeder insect for the pet and research industries and spread worldwide. They can be ...
) ballistic movements can be seen in the way they jump. The kicks that propel the cricket occur over a period of only 2-6ms, but during the 18-40ms prior to the kick the potential energy required is built up by the co-contraction of the antagonistic extensor and flexor tibiae. The crickets can also use these same ballistic movements for swimming.
Cone snail
In the cone snail (
Conus catus
''Conus catus'', common name the cat cone, is a species of sea snail, a marine gastropod mollusk in the family Conidae, the cone snails and their allies.
Like all species within the genus ''Conus'', these snails are predatory and venomous. T ...
) ballistic movement can be seen in the way that it fires is harpoon-like radular tooth into its prey. After the cone snail’s proboscis comes in contact with its prey the tooth is ejected 240-295 ms later. It is believed that the propulsion of the tooth is accomplished by pressurizing the fluid space behind the tooth.
Salamanders, toads, and chameleons
In
Salamanders
Salamanders are a group of amphibians typically characterized by their lizard-like appearance, with slender bodies, blunt snouts, short limbs projecting at right angles to the body, and the presence of a tail in both larvae and adults. All ten ...
,
Toads
Toad is a common name for certain frogs, especially of the family Bufonidae, that are characterized by dry, leathery skin, short legs, and large bumps covering the parotoid glands.
A distinction between frogs and toads is not made in scienti ...
, and
Chameleons
Chameleons or chamaeleons (family Chamaeleonidae) are a distinctive and highly specialized clade of Old World lizards with 202 species described as of June 2015. The members of this family are best known for their distinct range of colors, bein ...
ballistic movement can be seen in their tongue projection which is controlled by an elastic recoil mechanism. The orientation of the muscle fibers is significant because it is what allows ballistic movements to be possible. In chameleons, the
muscle fibers used for ballistic tongue movements were found to be in a spiral orientation, with an equal amount of fibers oriented clockwise and anti-clockwise to prevent torsional movement of the tongue during projection. The internal fiber angles are approximately 45 degrees, which is the theoretical optimum to create an equal strain throughout the accelerator muscles.
In salamanders of the genus
Hydromantes
''Hydromantes'', commonly referred to as web-toed salamanders, is a genus of the lungless salamander family, Plethodontidae; they achieve respiration through their skin and the tissues lining their mouth. They are endemic to mountains of Californ ...
, the pattern of muscle activation has been mapped. The main muscles used for ballistic tongue movements in these salamanders are the subarcualis rectus (SAR) muscles. These SAR muscles can be further divided into anterior (SARA) and posterior (SARP). The first muscle to be activated is the SARA, which is located near the back of the head. The SARA remains active until the tongue makes contact with the prey. Next, the posterior SARP, located further back on the medial and lateral sides of the salamander is activated. Then the middle SARP is activated and the anterior SARP is the last to be activated. The time between activation shortens and duration of activation increases with increasing prey distance. Ballistic tongues have evolved two times previously in the Hemidactyliini and Bolitoglossini genera. The exact mechanisms of tongue projection vary slightly throughout the taxa, but the resulting projections have remained relatively constant.
Frogs
A frog is any member of a diverse and largely carnivorous group of short-bodied, tailless amphibians composing the order Anura (ανοὐρά, literally ''without tail'' in Ancient Greek). The oldest fossil "proto-frog" '' Triadobatrachus'' is ...
do not have a specialized muscular structure for tongue projection. They are able to bypass this issue by using very rapid jaw movement to project the tongue forward. Present in all frogs are the two mandibular muscles that are used to control the jaw and, therefore, tongue projection. The m. genioglossus is used to protract the tongue and the m.hyoglossus is the tongue retractor. Both of these muscles have longitudinally oriented fibers, which is in contrast to the spiral oriented fibers of the chameleon.
Application in humans
In human, ballistic movements involve spontaneous propulsion of the limbs. This can be seen in daily routines such as reach and strike reactions, which are atomic by nature. Pointing gestures and placing an object are reach reactions; they have low acceleration and deceleration. On the other hand, punching and throwing are strike reactions; they are characterized by high acceleration and deceleration. These movements have highly variable target locations, and they are referred to as “ballistic” in
kinesiology
Kinesiology () is the scientific study of human body movement. Kinesiology addresses physiological, anatomical, biomechanical, pathological, neuropsychological principles and mechanisms of movement. Applications of kinesiology to human health ...
. During ballistic movement an initial impulse is needed to accelerate the limb (hand/foot) toward the target, then a decelerating impulse act as a brake to stop the movement. These movements are characterized by a bell-shaped velocity profile. The Bayesian Model(see
Bayesian network
A Bayesian network (also known as a Bayes network, Bayes net, belief network, or decision network) is a probabilistic graphical model that represents a set of variables and their conditional dependencies via a directed acyclic graph (DAG). Bay ...
), which was developed to perform recognition without pose-tracking, explains human ballistic movement as a sequence of movements between objects and the environment. Each movement is independent from precedent and subsequent one, in varying context. Fast single joints movement in humans is controlled by a series of activation of agonist, antagonist and then agonist muscles; this process is called triphasic activation. Those movements are executed “with a pattern of bursts in the agonist and antagonist muscles of fairly constant duration but different amplitude…” (Acornero et al. 1984).
[Accornero, N., Berardelli, A., Argenta, M. and Manfredi M. (1984). Two joints ballistic arm movements. Neuroscience Letters. 46: 91-95.] Any ballistic movement involving two joints will require an agonist and an antagonist burst; this can be viewed as the building blocks for different types of ballistic movements.
References
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Muscular system