The video clip below is from the History Channel program Human Weapon & gives a brief explanation of "Bursting" as it's called in Krav Maga as well as an application in Empty Hand vs a Knife.Keep in mind and remember that in a Real-World Defense situation,the target area's for the strike are primarily the Throat,Face or Eyes and You have to know Where Your going & What Your doing after the burst as well as have other options and back up plans that You can use/work in combination with this technique.
The Krav Burst concept shares many conceptual & technical characteristics with the S.P.E.A.R system and the two have many interchangeable aspects in My opinion and analysis of the two.The concept of Startle/Flinch response to surprise/sudden/ambush attacks,the 3 Natural Flinches in response to them of 1.Pushing away Danger,2.Head Shield/Covering Up and 3.Shield & Turn(Specific one depending on distance,direction of attack) that can & need to be "Educated" into something functional and effective apply to both methods although that is not necessarily the core concept of the Burst.The SPEAR manifests itself physically into two distinct types of SPEARS(but also can be anything in-between).One is the Tactical Spear,which is more aggressive,active and dynamic almost attacking the attacker(But ready to defend,react,evade etc. counters or changing dynamics)and the Defensive SPEAR which like it's namesake is defensive in nature and an educated cover/shielding movement when Your really caught off-guard to or some other evasive/defensive movement to allow You to transition to functional engagement methods or escape.
Like the SPEAR,I classify the BURST into a TACTICAL BURST and a DEFENSIVE BURST along the same lines as the differences described in the two SPEAR methods.The Tactical version is more aggressive and dynamic "attacking the attacker" and employs driving into the opponent with Upper Body or Leaning,shifting weight into them or even Shifting,Shuffling or Stepping Into them depending on distance and timing,but remaining prepared & ready to alter plan,evade,defend counters or react to changing circumstances.The Defensive Burst is one in Which Your caught off guard to a sudden surprise attack and don't have time to drive into them or You have to incorporate some evasive/defensive movement as well or even might involve moving away or to the side,so it's not as "offensive" or as forceful of an action as the Tactical version.And the Burst like the SPEAR can manifest itself as anything in-between the two extremes.
Keep in mind that The Educated Startle/Flinch & SPEAR/BURST Concepts can be applied & incorporated into virtually any technique or method as they are more Concepts or Principles rather then specific techniques,but if designing something to be an Educated Startle/Flinch response,then it really should be compatible/work with with natural startle/flinch responses,but what is Compatible with the Startle/Flinch as well as what constitutes a natural startle/flinch is open for argument/debatable as is the whole concept of the Blauer Startle/Flinch & SPEAR system which many consider a somewhat abstract,overly complex & not well defined/outlined system short on proven hard data & facts.The Burst by itself is a little more straight forward and easily demonstrable.You are in no way limited in Your options based on ones Man's idea of what is a natural startle/flinch response,So explore specific individual SF reactions Yourself and what You personally do as an individual.However,do so in combination with drawing,studying & researching that which has already been done by others."Don't re-invent the Wheel"as they say,but acknowledge anybody(even the so-called "experts")can be wrong and there are unique individuals & differences among people and specific responses may differ among specific individuals. I go over & explore some of different options in "Realistic Defense against a Knife"
Burst movements are usually simple movements that adapt well to educating the startle/flinch response although they are certainly formidable all by themselves at any time.Educated startle/flinch responses aren't just useful during an initial surprise sneak attack,but can be useful anytime during a violent engagement where Your caught off guard by something unexpected.The beauty of the Burst concept is that it shocks/stuns the opponent momentarily(although certainly could end the fight)acting as a bridge to Your next move which could be follow ups or escape.
I am not a real big believer in most claims of effectiveness of empty hand vs knife techniques as it is one of the toughest scenarios to be successful in and there simply isn't any actual,provable documentation of a particular individual who has been in a number of empty hand vs knife fight and been successful at least that I'm aware of currently.The primary goal is to escape,get to a weapon or draw Your own if You have one,preferable a firearm although the introduction and presentation of Your own knife can often diffuse the situation and deter the assailant.
S.P.E.A.R Article Part 1
S.P.E.A.R Article Part 2
Krav-Maga Knife Defense Article