What are the 4 phases in the 100m?

The 100-meter sprint is a 10-s race (men), making it hard for most observers to understand the event's sequence from start to finish. Coaches employ different racing strategies. Carl Lewis's coach Tom Tellez utilized 5 phases, but Maurice Greene's coach John Smith adopted 7 phases. 

The approaches used not only helps in creating an efficient execution of a sprint race and understanding the event better, but also allows for customized coaching strategies tailored to each athlete’s strengths and needs. Here, we can break down the 100m into four phases, based on biomechanical demands and what can be emphasized during the race.

The initial phase (0-10m)
This phase involves explosive and efficient movement from the blocks. The first 10m is very distinct from the other phases; the highest velocity generated is only at ~5 m/s (the next phase would be almost double). The acceleration tends to be highest at the beginning, as athletes need to overcome inertia for rapid forward movement. Thus, optimal block setting, efficient "clearance" (first steps), as well as smooth legs 'pumping' and arms 'swinging' are crucial. 

Technically, athletes need to keep a low center of gravity and lean forward to maximize horizontal force. The initial steps are short, lengthening as speed increases. Feet strike just behind the center of mass for optimal propulsion.

Early acceleration is critical; any delay can compromise the entire performance. Athletes may aim to quickly establish a leading position, and maintain an optimal strategy strategy. Note that when Usain Bolt broke the 100m world record (9.58s) in 2009, he was already leading by the 10m mark.

The drive phase (10-30m)
During this segment, athletes focus on generating substantial momentum by applying maximal force. This phase is similar to shifting a vehicle’s lower gear to maximize torque (high force production). 

Efficiency is important here to conserve energy for subsequent stages (e.g., avoid excessive "pumping" of the arms); the focus is generating momentum by exerting maximal force (within very short period) on the track. See the concept of rate of force development.

The maximal acceleration phase (30 to 50/60/70m)
This phase is where the speed is increasing from >90 to 100% of top velocity (thus, max acceleration). Sometimes, this phase is called "maximal velocity." Top velocity may be reached at later part of this phase, depending on one's ability. 

The critical transition here involves moving from a forward-leaning posture to an upright sprint, which would facilitate peak velocity (maximum speed) to be attained. For this reason, optimal execution is therefore imperative, as well as for sustaining the momentum generated earlier. 

Many top sprinters use this phase to differentiate themselves (ie, at 30-60m) among rivals of comparable early acceleration. 

The maintenance (50/60/70m to finish)
The final stage is characterized by the maintenance of velocity achieved in prior phases. The objective here is not to accelerate further, but to efficiently sustain velocity. 

The ability to decelerate less than competitors during this phase often results in overtaking opponents towards the finish. 

Here, a proper sprinting form is crucial; otherwise, poor technique can affect coordination, influencing stride length and cadence. This may lead to longer ground contact times, which can slow athletes down and reduce their push-off ability.

Final thought ...
Each phase is integral to the race's overall strategy and requires meticulous execution to optimize performance outcomes. 

For optimizing understanding of performance and coaching, it is important to record data (i.e., during competitions) at key intervals: at 10m to evaluate early acceleration, at 30m to assess the drive phase (10-30m splits), at 60m (30-60m) to assess maximal velocity, and from 60 to 100 meters to analyze the maintenances. This approach helps in refining racing and training strategies, and therefore, improve sprint performance.