A trainer that changes the resistance to match the road you’re on in Zwift. You pair it with Zwift through Bluetooth. 
 
Then when you’re going up a hill, or if the road surface changes from tarmac to gravel, you’ll feel the resistance increase. 
 
It makes it much more like riding in real life.

Your Smart Trainer will tell Zwift how much power you’re producing, measured in Watts.
 
Zwift combines that with your weight to determine how fast you’re going. 
 
A heavy rider will need to put out more Power than a light rider to travel at the same speed. So what matters isn’t Watts, it’s Watts per kilogramme.

Zwift thinks about Power in Zones. As you ride, you’ll see a coloured graph build up at the bottom of the screen, showing which zones you’ve been riding in for the last 10 minutes. 
 
The Zones aren’t set at an absolute level. Rather, they are worked out for each person relative to their own capabilities, and they are colour coded. 
 
Blue is power you could pretty much sustain all day long, as long as you kept eating and drinking. Yellow is fairly hard work. Red you might be able to sustain for a minute or two. 
 
Zwift needs a way to decide where your Zones are. It does it by calculating percentages of your FTP:
 

Functional Threshold Power. Technically, it’s the maximum average power you can put out for an hour. Practically, it’s a measure of how strong and fit you are.
 
Knowing (roughly) your FTP is important if you want to do a Workout. It enables Zwift to adjust the power targets to reflect your fitness level, and this stops the workout being too hard or pointlessly easy.
 
There are several ways to find out what your FTP is, and happily they don’t involve spending an hour at maximum power. 
 
Zwift has a couple of workouts designed to identify it. 
 
Alternatively, just go for a ride and keep an eye on the power you’re producing. Find a level where you’re putting some effort in, but you feel you could sustain it for ages. Stick at it for 5 minutes and if you’re still breathing easily, that’s probably in your Blue zone. Make a note of the power, multiply it by 1.5 and try that as your FTP. 
 
It’s easy to adjust if it turns out to be too high or too low. Getting it roughly right is good enough. 
 
Finally, your FTP changes with your fitness level. If you ride regularly, it will go up. If you take a few weeks off, it will go down. You’ll get a feel for it. And Zwift will prompt you if it detects that your FTP has increased.
 
There’s more about FTP in Zwift here: LINK

The idea of a Workout is a bit like having a personal trainer – rather than letting you cruise around aimlessly, you have a set amount of exercise to get through. 
 
Zwift comes with lots of Workouts that you can choose from, of different lengths and intensities. Zwift uses your FTP to adjust the Workout so that it suits your level of fitness. Two riders of different levels of fitness will have to work equally hard to complete a workout. 
 
Workouts are divided into Intervals. For each Interval, Zwift will tell you how much Power you should be putting out. Sometimes it will also tell you what Cadence to ride at. 
 
Generally, the first interval is a Warm Up. Often this gets gradually harder to ease you into the ride, and sometimes includes some short bursts of higher power work to wake your legs up.
 
The following Intervals will have a Power target for you to hit. If you succeed in hitting the target power, you earn a Star for that Interval.
 
The last Interval in the Workout is normally a Cool Down, for you to spend relaxing and feeling pleased with yourself for having hit all the Stars.

How fast your legs are moving – measured in Revolutions per Minute (rpm). It’s worth getting a Cadence sensor to fit to your bike and connect to Zwift over Bluetooth.
 
At any given level of power, higher cadences work the heart harder, and produce a higher Heart Rate. Lower cadences rely more on strength.
 
Aiming at a cadence of 80-90 rpm is efficient, in that it uses a mix of fast and slow twitch muscle fibres. That’s a faster rate than most people would naturally ride at, particularly people with Parkinson’s, and it can take some getting used to. Practicing riding at a higher cadence is a good thing to build into your routine.

This is useful if you’re doing a Workout. As you choose the Workout, at the bottom of the screen there’s an option to use ERG mode.
 
When you ride normally in Zwift using a Smart Trainer and you feel the resistance change, you change gear as you would when riding on the road. That enables you to keep to a cadence that feels comfortable. 
 
If you’re doing a Workout, and the required power goes up, you either need to increase your cadence, select a higher gear, or a bit of both. 
 
When you do a Workout in ERG mode, Zwift does all the gear changing for you. You decide what cadence you want to ride at, and Zwift gets your Smart Trainer to change the resistance level to ensure that you’re delivering the required amount of power. There is nowhere to hide.
 
(Well, there is. If you’re finding it too hard, you can reduce the FTP Bias in the Companion App. That will last for the rest of the workout. If you generally find it too hard, try reducing your FTP.)

Two main things determine the speed you’re going at. The power you’re putting out, in W/kg, and the road conditions – particularly whether it’s uphill, downhill or flat.
 
Other things get taken into account too: some bikes in Zwift are more aerodynamic than others; roads made of Gravel and Sand are slower than Tarmac.

For Club Events – Workouts, or Meet Ups – we generally have Keep Together turned on. That means we ride as a group, with Zwift restraining the quickest and boosting the slowest so that we stick together. It makes it more sociable.  

If you’ve got enough devices, it’s worth running the Zwift Companion app on your phone. 
 
While you’re riding, it gives you extra information – a map, details of the Workout you’re doing, a list of the riders nearby. 
 
It also gives you some extra controls for the Zwift game, and allows you to send humorous or supportive messages to other riders, which appear on screen. 
 
For this to work, the devices that are running Zwift and Zwift Companion need to be on the same Wi-fi network. 
 
Zwift Companion is useful when you’re not riding too. In particular, it enables you to join the ZWAP club, and then to sign up for Club Events.
 
Finally, Zwift Companion can take you into the murky world of the Zwift Forum, where you can find out about game updates, and what the (sometimes grumpy) user base think about them.
 
There’s more about Zwift Companion on the Zwift website, here: LINK

It’s optional, but if you’re exercising seriously for Parkinson’s, it’s good to monitor your heart rate.  
 
There are many makes of HRM available. They’re either a strap that you wear across your chest, or a band that goes around your arm. They pass your Heart Rate to Zwift, which then displays it, and also plots it as a red line at the bottom of the ride screen next to the chart of your recent power output.