Whether you are throwing a 90-pound ruck on your back, carrying those tools around the job site, or refilling the water cooler at the office having a strong back is essential to life. We don't believe in having a glass back we believe in having a capable back. You will flex, extend, and have to move in all sorts of odd positions (try helping your buddy move furniture without being in all sorts of fun positions) therefore we need to train our back under load in various positions. If you are still of mind we should never "flex our spines in training" I'd highly suggest looking at current information regarding lifting techniques such as the following as just a start even though there is much more than this; Mawston et al., (2021) PMID: 33799053, Saraceni et al., (2021) PMID: 34288926. Long story short, our spine and back musculature as well as all ancillary tissues are incredible and capable units that can adapt over time and become more and more resilient. So with all of these exercise recommendations start slow, start light, and watch lots of videos. Here are 4 of my current go-to back/posterior chain training exercises you may want to throw into your routine:
1. Romanian Deadlifts - A Fantastic hinge movement that's going to develop those erector spinae musculature, hamstrings, and hip extensors such as the glutes. I slightly prefer the Romanian deadlift over a stiff leg deadlift as during the set barbell does not touch the ground and tension is maintained through the posterior chain.
2. Reverse Hyper Machine - If your gym does not have one of these I would try to find one of these. Invented by the legendary Louie Simmons this machine can really be used for a lot of skill levels in the gym and anecdotally it helped build my deadlift from 515 to 585 as an accessory movement.
3. Jefferson Curls - Requires the spine to go into flexion and return to a standing position. Highly recommend watching a few videos before utilizing them and starting very light (I began with body weight for a week). This is one of those exercises that's going to push you into a range of motion you may not be super developed in.
4. Good Mornings - One of the OG backbuilders. Barbell on the back, hinge at the hips, and bend over; it's simple, brutal, and I love it. Start light, get a feel for the motion, and enjoy the back pump.