Lateral Stretch

A lateral stretch refers to an extension of the index finger toward the center of the keyboard while the middle finger stays stationary, or an extension of the pinky finger toward the side of the keyboard while the ring finger stays stationary.

Note

In anatomical terms, a lateral stretch is an index abduction or a pinky adduction that occurs while the adjacent finger (middle or ring) remains stationary.

Some people find this motion uncomfortable and seek a keyboard layout that minimizes it.

On Colemak, for example, a common complaint is that typing “the,” the most common word in English, requires the index finger to stretch toward the h at the same time the middle finger reaches for e:

base

shift

However, not all people agree that minimizing lateral stretches should be prioritized. Pianists and guitarists have no trouble abducting and adducting their fingers in all sorts of different ways.

Explicit-event analysis semantics

Layouts Wiki analyzes keymaxx’s explicit press, hold-acquisition, and hold-release events. Lateral stretch describes posture, so every event’s posture contains both its physical action keys and its sustained keys. Simultaneous lateral-stretch unigrams compare every unordered pair within one event’s posture. Bigrams compare every posture key at the first event with every posture key at the second, and skipgrams do the same at the first and third events. A steady hold participates for as long as that posture is maintained.

Headline totals such as LSB and LSS1 count each bigram or trigram at most once. The structured lateral stretch breakdowns are involvement buckets by ulnar finger, radial finger, and distance; their sums may not partition the headline total when one n-gram involves multiple lateral-stretch pairs. Legacy finger-pair fields are ulnar-finger involvement buckets only, so consumers that need the full pair and distance should use the structured lateral stretch fields.

Lateral Stretch Bigram

A lateral stretch bigram (LSB) is a bigram that creates a lateral stretch motion between adjacent fingers. Unlike scissors which are classified by distance, all lateral stretches are counted equally as long as they meet the minimum radioulnar distance requirement.

$\text{LSB}\% = \frac{\text{\# of lateral stretch bigrams}}{\text{\# of bigrams}}$

For a bigram to qualify as a lateral stretch:

• The radioulnar distance between the two fingers must be at least 2u (1u beyond the normal adjacent finger spacing)
• One finger must move laterally while the adjacent finger remains in its home columns

Lateral stretches are considered uncomfortable due to the lateral extension required, which can strain the hand and reduce typing comfort. The severity varies by finger pair:

• Index-middle stretches: Index finger extends toward center while middle stays in home columns
• Ring-pinky stretches: Pinky finger extends outward while ring stays in home columns

Note

Middle-ring stretches are tracked internally but not displayed in finger breakdowns, as they are anatomically less significant and less common in typical typing patterns.

Examples

On QWERTY:

• th creates an index stretch: index moves to h (column 6) while middle stays at e (column 3)
• az creates a pinky stretch: pinky moves to z (column 2) while ring stays at s (column 3)

Lateral Stretch Skipgram

A lateral stretch skipgram (LSS) is a skipgram that creates a lateral stretch motion between adjacent fingers. Like LSB, these require a minimum 2u radioulnar distance between the fingers.

$\text{LSS}_1\% = \frac{\text{\# of 1st order lateral stretch skipgrams}}{\text{\# of trigrams}}$

Lateral stretch skipgrams capture uncomfortable patterns where the lateral stretch happens with an intervening keypress, such as “t_e” in “the” on Colemak. While less severe than direct lateral stretches, they can still impact typing comfort.

Sources

“Lateral stretches,” Keyboard Layouts Doc (3rd edition)