Neostigmine is a drug that acts to inhibit acetylcholinesterase. When compared to the absence of the drug, the effect of neostigmine on skeletal muscle will be

Neostigmine, by inhibiting acetylcholinesterase, prevents the breakdown of acetylcholine in the synaptic cleft. Acetylcholine is a neurotransmitter that transmits signals from nerves to muscles, causing muscle contraction.

In the absence of neostigmine, acetylcholine is broken down by acetylcholinesterase after it has transmitted the signal for muscle contraction, allowing the muscle to relax.

When neostigmine is present, it inhibits acetylcholinesterase, so acetylcholine is not broken down as quickly. This means that more acetylcholine is available in the synaptic cleft to transmit signals for muscle contraction.

Therefore, the effect of neostigmine on skeletal muscle will be to increase muscle contraction and reduce muscle relaxation. This can lead to increased muscle tone and potentially muscle fatigue if the drug is present in high amounts.