More specialized zips, like the ones Welga used, created secondary and tertiary effects. They could deliver additional ions or acetylcholine to neuromuscular junctions. Either one would speed up the communication between peripheral neurons and the brain. Some could improve the synchronization across different types of muscle fibers.

Other advantages came from long-term changes: to the muscle fiber composition; to the density of neurotransmitters, cell membrane gates, and receptors; to the amount of oxygen a muscle fiber could store; to improved heart and lung function. Someone like Welga, who spent a lot of time training her body, would have advantages that no zip could mimic. And—or so Nithya suspected—people who worked in military special forces had access to advanced biogenetic engineering that general queries wouldn’t reveal.

Any intense activity had a price, though. Muscles needed to recover. Transmitters needed to be taken back into cells or released. Electric potentials needed to be restored. Those processes could also be accelerated, but physics would eventually take over. Long-term, sustained rapid muscle activation wasn’t possible… yet. Pill funders had plenty of projects going to find solutions to that.

In the meantime, fifteen to thirty minutes of zip-fueled activity—like the fights Welga engaged in—could leave behind badly damaged cells. That was where juvers helped. Some of Nithya’s first projects related to muscle-fiber rejuvenation. Later designs acted as prophylactics if the user took them at the correct time. According to Sita’s reports, the dominant research at the moment focused on mitogens. Those could stimulate the reproduction of satellite cells, the first step in the chain of skeletal muscle repair. Welga had once described the zip comedown to Nithya as a combination of hangover and soreness, almost like having the flu. The new, mitogenic class of juver would reduce or eliminate that effect.

Nithya sat back, digesting the information. Welga’s symptoms pointed at hyperexcitation, but none of the data on the newest juver or zip designs showed that as a side effect. It had been common in the early days, sending people into uncontrollable twitching or cramping. The kind of large-scale tremor that Nithya saw in Welga usually indicated a problem at the source: in the brain. But Welga’s biodata showed a correlation between zip usage and involuntary movement in her limbs. It contained no information about other areas of her body.

“Sita, send a request to Welga’s agent for cerebral activity logs. If they don’t exist, ask if Welga can take some diagnostic pills to monitor that region.”

“I’ve sent the request. Reminder: Your gynecologist appointment is in five minutes.”

Nithya expanded her view of Luis’s feed. He stood next to an engine with tools strewn on the floor and his body swathed in a clean-room suit. She opened an audio channel to him.

“You look busy,” she said, keeping her tone light to hide her irritation. She had assumed he’d be at the hospital with Welga.