It's the hardest time to work out--you're the heaviest, you're the most off-balance, any aches and pains come out now, energy is hard to come by, you're busy preparing for baby's arrival--but it's critical to exercise through the 3rd trimester up until delivery!
I continued toprope climbing until 2 weeks before I gave birth and weightlifting until 2 days before I gave birth. I attribute my relatively easy labor & recovery and my relatively few pregnancy symptoms to working out till the end. The worst symptoms I had in my 3rd trimester were bruised-feeling ribs, likely due to my baby's feet pressing on my ribcage (it went away right after delivery), constipation, increasingly squashed internal organs, and minor leg swelling in the last 2 weeks. Not bad!
normal vs. common
The 3rd trimester, when you're at your highest weight gain, is when you typically hear mothers complain about aching backs, pelvic floor pain, cramping, swelling. Quick Google searches or asking the doctor about symptoms almost 100% of the time is returned with "don't worry, that's normal."
Normal has the connotation that it's natural and there's nothing that can be done. You: "My lower back is really aching." Doctor: "That's totally normal at this point, since your baby's getting so much larger and throwing off your center of gravity." It implies that you deal with the pain rather than dig into what can be done.
Common, on the other hand, has the connotation that it's widespread, but leaves a door open that something can be done.
Framing your aches and pains as common rather than normal, and putting the time into research and action to correct your pains, will go a huge way to your comfort!
the 3rd trimester is the most critical time to continue exercising
You need strong abdominals for the end game: labor. Imagine stopping exercising or firing muscles for 3 months--they'll atrophy! Plus in the 3rd trimester you need strong abdominals and trunk to support the offset weight of a baby. Sure, listen to your body to dial back your max sets/reps/weight, but if you've been lifting until now, no reason to stop! There's ample evidence that exercising to 60%+ of your max through delivery has very positive labor outcomes for both mom and baby (I have a more dedicated research article coming on this).
Aches and pains are likely attributed poor posture and declining attention to proper body mechanics. There are a set of issues that will only be resolved with popping that baby out, like bruised ribs and swelling, but most everything else can at least be mitigated. Check your body posture: are you compensating for a big belly with a pelvic tilt, rather than having a neutral pelvis and spine? Are you sticking your chest out? Do still brace your core at 20% when you're standing to support your belly? Do you do some bit of standing each day, or do you resort to sitting and lounging? Have you done prenatal yoga?
I highly recommend Deskbound: Standing up to a Sitting World for anyone in general, pregnant or not, to check your body mechanics in everyday life. Understand the principles of proper posture and mechanics, then adapt that to a pregnant body. If you're more sports inclined, you can get the same info applied more to sports in Becoming a Supple Leopard.
By the scale, I gained 21lb, though I lost at least 3-4lb of muscle, putting my total weight gain at ~25lb.
I settled into working out 3 days a week in the 3rd trimester, a day each of weightlifting, toprope climbing, and prenatal yoga per week. I recommend:
- Core: Transverse Abdominis is key. It's the most inner layer of abdominal muscles (not the 6-pack abdominals), and kettlebell windmills, squats, and deadlifts were my go-tos. The transverse abdominis prevents diastasis recti (a vertical splitting of your abdominal wall after pregnancy) and is the foundation for functional strength, pregnancy aside.
- Cardio: Even if it's a boring stair stepper, or a hike, or climbing, get your blood going. I got my heartrate up to 160bpm for a few minutes.
- Functional activity: choose your favorite, whether it's climbing or prenatal yoga or hiking! If nothing else, it'll keep your spirits up!