Calling a property of a struct with a placeholder?

I have a few places in my app where I need to alter a property of a struct, but it takes a lot of code.

The struct, arrays and variables:

Code Block 
struct Horse {
	var name: String
    var basicTraining : Float
    var rhythm : Float
    var suppleness : Float
var myHorses = [ 
Horse(name: "Donnerhall", basicTraining : 0.5, rhythm : 0.2, suppleness : 0.1),
Horse(name: "Bjork", basicTraining : 0.4, rhythm : 0.3, suppleness : 0.1)
]
var horseIndex = 0
var scaleCode = [ basicSkills, rhythmSkills, supplenessSkills ]
var currentScaleCode = basicSkills
var skillIndex = 0

The current code (takes a lot of lines):

Code Block 
func trainHorse() {
if myHorses[horseIndex].basicTraining > 100 {
                myHorses[horseIndex].basicTraining = 100 }
 if myHorses[horseIndex].basicTraining < 100 {
                myHorses[horseIndex].basicTraining += currentScaleCode[skillIndex].basicBoost }
            
            if myHorses[horseIndex].rhythm > 100 {
                myHorses[horseIndex].rhythm = 100 }
            if myHorses[horseIndex].rhythm < 100 {
                myHorses[horseIndex].rhythm += currentScaleCode[skillIndex].rhythmBoost }
            if myHorses[horseIndex].suppleness > 100 {
                myHorses[horseIndex].suppleness = 100 }
            if myHorses[horseIndex].suppleness < 100 {
                myHorses[horseIndex].suppleness += currentScaleCode[skillIndex].supplenessBoost }
}

What I would like is to simplify this code by doing something like this:

Code Block 
var currentTraining = basicTraining //or rhythm or suppleness
currentBoost = basicBoost
func trainHorse() {
if myHorses[horseIndex].currentTraining > 100 {
                myHorses[horseIndex].currentTraining = 100 }
 if myHorses[horseIndex].currentTraining < 100 {
                myHorses[horseIndex].currentTraining += currentScaleCode[skillIndex].currentBoost }

But when I call a property using a placeholder, I get the error "Value of type 'Horse' has no member..." I have tried using different types of brackets and parentheses without luck

Code Block 
import Foundation
struct Horse {
    var name: String
    var basicTraining : Float
    var rhythm : Float
    var suppleness : Float
}
var myHorses = [
    Horse(name: "Donnerhall", basicTraining : 0.5, rhythm : 0.2, suppleness : 0.1),
    Horse(name: "Bjork", basicTraining : 0.4, rhythm : 0.3, suppleness : 0.1)
]
var horseIndex = 0
var currentTraining: WritableKeyPath<Horse, Float> = \.basicTraining //or \.rhythm or \.suppleness
func trainHorse() {
    if myHorses[horseIndex][keyPath: currentTraining] > 100 {
        myHorses[horseIndex][keyPath: currentTraining] = 100
    }
    if myHorses[horseIndex][keyPath: currentTraining] < 100 {
        myHorses[horseIndex][keyPath: currentTraining] += currentScaleCode[skillIndex].basicBoost
    }
    //...
}